1 Introduction

This document describes the SCA Assembly Model, which covers

· A model for the assembly of services, both tightly coupled and loosely coupled

· A model for applying infrastructure capabilities to services and to service interactions, including Security and Transactions

The document starts with a short overview of the SCA Assembly Model.

The next part of the document describes the core elements of SCA, SCA components and SCA composites.

The final part of the document defines how the SCA assembly model can be extended.

This specification is defined in terms of Infoset and not in terms of XML 1.0, even though the specification uses XML 1.0 terminology. A mapping from XML to infoset is trivial and it is suggested that this is used for any non-XML serializations.

1.1 Terminology

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

1.2 Normative References

[RFC2119]

S. Bradner, Key words for use in RFCs to Indicate Requirement Levels,

IETF RFC 2119, March 1997.

http://www.ietf.org/rfc/rfc2119.txt

[SCA-Java]

OASIS Committee Draft 02, "SCA POJO Component Implementation Specification Version 1.1", February 2010

http://docs.oasis-open.org/opencsa/sca-j/sca-javaci-1.1-spec.pdf

[SCA-Common-Java]

OASIS Committee Draft 04, "SCA Java Common Annotations and APIs Specification Version 1.1", February 2010

http://docs.oasis-open.org/opencsa/sca-j/sca-javacaa-1.1-spec.pdf

[SCA BPEL]

OASIS Committee Draft 02, "SCA WS-BPEL Client and Implementation Specification Version 1.1", March 2009

http://docs.oasis-open.org/opencsa/sca-bpel/sca-bpel-1.1-spec.pdf

[SDO]

OASIS Committee Draft 02, "Service Data Objects Specification Version 3.0", November 2009
http://www.oasis-open.org/committees/download.php/35313/sdo-3.0-cd02.zip

[JAX-WS]

JAX-WS Specification

http://jcp.org/en/jsr/detail?id=224

[WSI-BP]

WS-I Basic Profile

http://www.ws-i.org/deliverables/workinggroup.aspx?wg=basicprofile

[WSI-BSP]

WS-I Basic Security Profile

http://www.ws-i.org/deliverables/workinggroup.aspx?wg=basicsecurity

[WS-BPEL]

OASIS Standard, "Web Services Business Process Execution Language Version 2.0", April 2007

http://docs.oasis-open.org/wsbpel/2.0/wsbpel-v2.0.pdf

[WSDL-11]

WSDL Specification version 1.1

http://www.w3.org/TR/wsdl

[SCA-WSBINDING]

OASIS Committee Draft 04, "SCA Web Services Binding Specification Version 1.1", May 2010

http://docs.oasis-open.org/opencsa/sca-bindings/sca-wsbinding-1.1-spec.pdf

[SCA-POLICY]

OASIS Committee Draft 03, "SCA Policy Framework Specification Version 1.1", May 2010

http://docs.oasis-open.org/opencsa/sca-policy/sca-policy-1.1.pdf

[SCA-JMSBINDING ]

OASIS Committee Draft 04, "SCA JMS Binding Specification Version 1.1 Version 1.1", May 2010

http://docs.oasis-open.org/opencsa/sca-bindings/sca-jmsbinding-1.1-spec.pdf

[SCA-CPP-Client]

OASIS Committee Draft 05, "SCA Client and Implementation for C++ Specification Version 1.1", March 2010

http://docs.oasis-open.org/opencsa/sca-c-cpp/sca-cppcni-1.1-spec.pdf

[SCA-C-Client]

OASIS Committee Draft 05, "SCA Client and Implementation for C Specification Version 1.1", March 2010

http://docs.oasis-open.org/opencsa/sca-c-cpp/sca-ccni-1.1-spec.pdf

[ZIP-FORMAT]

ZIP Format Definition

http://www.pkware.com/documents/casestudies/APPNOTE.TXT

[XML-INFOSET]

Infoset Specification

http://www.w3.org/TR/xml-infoset/

[WSDL11_Identifiers]

WSDL 1.1 Element Identiifiers

http://www.w3.org/TR/wsdl11elementidentifiers/

1.3 Non-Normative References

N/A

1.4 Naming Conventions

This specification follows naming conventions for artifacts defined by the specification:

· For the names of elements and the names of attributes within XSD files, the names follow the CamelCase convention, with all names starting with a lower case letter.
e.g. <element name="componentType" type="sca:ComponentType"/>

· For the names of types within XSD files, the names follow the CamelCase convention with all names starting with an upper case letter.
eg. <complexType name="ComponentService">

· For the names of intents, the names follow the CamelCase convention, with all names starting with a lower case letter, EXCEPT for cases where the intent represents an established acronym, in which case the entire name is in upper case.
An example of an intent which is an acronym is the "SOAP" intent.

2 Overview

Service Component Architecture (SCA) provides a programming model for building applications and solutions based on a Service Oriented Architecture. It is based on the idea that business function is provided as a series of services, which are assembled together to create solutions that serve a particular business need. These composite applications can contain both new services created specifically for the application and also business function from existing systems and applications, reused as part of the composition. SCA provides a model both for the composition of services and for the creation of service components, including the reuse of existing application function within SCA composites.

SCA is a model that aims to encompass a wide range of technologies for service components and for the access methods which are used to connect them. For components, this includes not only different programming languages, but also frameworks and environments commonly used with those languages. For access methods, SCA compositions allow for the use of various communication and service access technologies that are in common use, including, for example, Web services, Messaging systems and Remote Procedure Call (RPC).

The SCA Assembly Model consists of a series of artifacts which define the configuration of an SCA Domain in terms of composites which contain assemblies of service components and the connections and related artifacts which describe how they are linked together.

One basic artifact of SCA is the component, which is the unit of construction for SCA. A component consists of a configured instance of an implementation, where an implementation is the piece of program code providing business functions. The business function is offered for use by other components as services. Implementations can depend on services provided by other components – these dependencies are called references. Implementations can have settable properties, which are data values which influence the operation of the business function. The component configures the implementation by providing values for the properties and by wiring the references to services provided by other components.

SCA allows for a wide variety of implementation technologies, including "traditional" programming languages such as Java, C++, and BPEL, but also scripting languages such as PHP and JavaScript and declarative languages such as XQuery and SQL.

SCA describes the content and linkage of an application in assemblies called composites. Composites can contain components, services, references, property declarations, plus the wiring that describes the connections between these elements. Composites can group and link components built from different implementation technologies, allowing appropriate technologies to be used for each business task. In turn, composites can be used as complete component implementations: providing services, depending on references and with settable property values. Such composite implementations can be used in components within other composites, allowing for a hierarchical construction of business solutions, where high-level services are implemented internally by sets of lower-level services. The content of composites can also be used as groupings of elements which are contributed by inclusion into higher-level compositions.

Composites are deployed within an SCA Domain. An SCA Domain typically represents a set of services providing an area of business functionality that is controlled by a single organization. As an example, for the accounts department in a business, the SCA Domain might cover all financial related function, and it might contain a series of composites dealing with specific areas of accounting, with one for customer accounts, another dealing with accounts payable. To help build and configure the SCA Domain, composites can be used to group and configure related artifacts.

SCA defines an XML file format for its artifacts. These XML files define the portable representation of the SCA artifacts. An SCA runtime might have other representations of the artifacts represented by these XML files. In particular, component implementations in some programming languages might have attributes or properties or annotations which can specify some of the elements of the SCA Assembly model. The XML files define a static format for the configuration of an SCA Domain. An SCA runtime might also allow for the configuration of the Domain to be modified dynamically.

2.1 Diagram used to Represent SCA Artifacts

This document introduces diagrams to represent the various SCA artifacts, as a way of visualizing the relationships between the artifacts in a particular assembly. These diagrams are used in this document to accompany and illuminate the examples of SCA artifacts and do not represent any formal graphical notation for SCA.

Figure ‎2‑1 illustrates some of the features of an SCA component:

Figure ‎2‑1: SCA Component Diagram

Figure ‎2‑2 illustrates some of the features of a composite assembled using a set of components:

Figure ‎2‑2: SCA Composite Diagram

Figure ‎2‑3 illustrates an SCA Domain assembled from a series of high-level composites, some of which are in turn implemented by lower-level composites:

Figure ‎2‑3: SCA Domain Diagram

3 Implementation and ComponentType

Component implementations are concrete implementations of business function which provide services and/or which make references to services provided elsewhere. In addition, an implementation can have some settable property values.

SCA allows a choice of any one of a wide range of implementation types, such as Java, BPEL or C++, where each type represents a specific implementation technology. The technology might not simply define the implementation language, such as Java, but might also define the use of a specific framework or runtime environment. Examples include SCA Composite, Java implementations done using the Spring framework or the Java EE EJB technology.

Services, references and properties are the configurable aspects of an implementation. SCA refers to them collectively as the component type.

Depending on the implementation type, the implementation can declare the services, references and properties that it has and it also might be able to set values for all the characteristics of those services, references and properties.

So, for example:

· for a service, the implementation might define the interface, binding(s), a URI, intents, and policy sets, including details of the bindings

· for a reference, the implementation might define the interface, binding(s), target URI(s), intents, policy sets, including details of the bindings

· for a property the implementation might define its type and a default value

· the implementation itself might define policy intents or concrete policy sets

The means by which an implementation declares its services, references and properties depend on the type of the implementation. For example, some languages like Java, provide annotations which can be used to declare this information inline in the code.

Most of the characteristics of the services, references and properties can be overridden by a component that uses and configures the implementation, or the component can decide not to override those characteristics. Some characteristics cannot be overridden, such as intents. Other characteristics, such as interfaces, can only be overridden in particular controlled ways (see the Component section for details).

3.1 Component Type

Component type represents the configurable aspects of an implementation. A component type consists of services that are offered, references to other services that can be wired and properties that can be set. The settable properties and the settable references to services are configured by a component that uses the implementation.

An implementation type specification (for example, the WS-BPEL Client and Implementation Specification Version 1.1 [SCA BPEL]) specifies the mechanism(s) by which the component type associated with an implementation of that type is derived.

Since SCA allows a broad range of implementation technologies, it is expected that some implementation technologies (for example, the Java Component Implementation Specification Version 1.1 [SCA-Java]) allow for introspecting the implementation artifact(s) (for example, a Java class) to derive the component type information. Other implementation technologies might not allow for introspection of the implementation artifact(s). In those cases where introspection is not allowed, SCA encourages the use of a SCA component type side file. A component type side file is an XML file whose document root element is sca:componentType.

The implementation type specification defines whether introspection is allowed, whether a side file is allowed, both are allowed or some other mechanism specifies the component type. The component type information derived through introspection is called the introspected component type. In any case, the implementation type specification specifies how multiple sources of information are combined to produce the effective component type. The effective component type is the component type metadata that is presented to the using component for configuration.

The extension of a componentType side file name MUST be .componentType. [ASM40001] The name and location of a componentType side file, if allowed, is defined by the implementation type specification.

If a component type side file is not allowed for a particular implementation type, the effective component type and introspected component type are one and the same for that implementation type.

For the rest of this document, when the term 'component type' is used it refers to the 'effective component type'.

Snippet ‎3‑1 shows the componentType pseudo-schema:

<?xml version="1.0" encoding="ASCII"?>

<service … />*

<reference … />*

<property … />*

<implementation … />?

</componentType>

Snippet ‎3‑1: componentType Pseudo-Schema

The componentType element has the child elements:

· service : Service (0..n) – see component type service section.

· reference : Reference (0..n) – see component type reference section.

· property : Property (0..n) – see component type property section.

· implementation : Implementation (0..1) – see component type implementation section.

3.1.1 Service

A Service represents an addressable interface of the implementation. The service is represented by a service element which is a child of the componentType element. There can be zero or more service elements in a componentType. Snippet ‎3‑2 shows the componentType pseudo-schema with the pseudo-schema for a service child element:

<?xml version="1.0" encoding="ASCII"?>

<service name="xs:NCName"

requires="list of xs:QName"? policySets="list of xs:QName"?>*

<binding … />*

<callback>?

<binding … />+

</callback>

<requires/>*

<policySetAttachment/>*

</service>

<reference … />*

<property … />*

<implementation … />?

</componentType>

Snippet ‎3‑2: componentType Pseudo-Schema with service Child Element

The service element has the attributes:

· name : NCName (1..1) - the name of the service. The @name attribute of a <service/> child element of a <componentType/> MUST be unique amongst the service elements of that <componentType/>. [ASM40003]

· requires : listOfQNames (0..1) - a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets : listOfQNames (0..1) - a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The service element has the child elements:

· interface : Interface (1..1) - A service has one interface, which describes the operations provided by the service. For details on the interface element see the Interface section.

· binding : Binding (0..n) - A service element has zero or more binding elements as children. If the binding element is not present it defaults to <binding.sca>. Details of the binding element are described in the Bindings section.

· callback (0..1) / binding : Binding (1..n) - A callback element is used if the interface has a callback defined, and the callback element has one or more binding elements as subelements. The callback and its binding subelements are specified if there is a need to have binding details used to handle callbacks. If the callback element is not present, the behaviour is runtime implementation dependent. For details on callbacks, see the Bidirectional Interfaces section.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

· policySetAttachment : policySetAttachment (0..n) - A service element has zero or more policySetAttachment subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

3.1.2 Reference

A Reference represents a requirement that the implementation has on a service provided by another component. The reference is represented by a reference element which is a child of the componentType element. There can be zero or more reference elements in a component type definition. Snippet ‎3‑3 shows the componentType pseudo-schema with the pseudo-schema for a reference child element:

<?xml version="1.0" encoding="ASCII"?>

<service … />*

<reference name="xs:NCName"

autowire="xs:boolean"?

multiplicity="0..1 or 1..1 or 0..n or 1..n"?

wiredByImpl="xs:boolean"? requires="list of xs:QName"?

policySets="list of xs:QName"?>*

<binding … />*

<callback>?

<binding … />+

</callback>

<requires/>*

<policySetAttachment/>*

</reference>

<property … />*

<implementation … />?

</componentType>

Snippet ‎3‑3: componentType Pseudo-Schema with reference Child Element

The reference element has the attributes:

· name : NCName (1..1) - the name of the reference. The @name attribute of a <reference/> child element of a <componentType/> MUST be unique amongst the reference elements of that <componentType/>. [ASM40004]

· multiplicity : 0..1|1..1|0..n|1..n (0..1) - defines the number of wires that can connect the reference to target services. The multiplicity can have the following values

– 0..1 – zero or one wire can have the reference as a source

– 1..1 – one wire can have the reference as a source

– 0..n - zero or more wires can have the reference as a source

– 1..n – one or more wires can have the reference as a source

If @multiplicity is not specified, the default value is "1..1".

· autowire : boolean (0..1) - whether the reference is autowired, as described in the Autowire section. Default is false.

· wiredByImpl : boolean (0..1) - a boolean value, "false" by default. If set to "false", the reference is wired to the target(s) configured on the reference. If set to "true" it indicates that the target of the reference is set at runtime by the implementation code (e.g. by the code obtaining an endpoint reference by some means and setting this as the target of the reference through the use of programming interfaces defined by the relevant Client and Implementation specification). If @wiredByImpl is set to "true", then any reference targets configured for this reference MUST be ignored by the runtime. [ASM40006]

· requires : listOfQNames (0..1) - a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets : listOfQNames (0..1) - a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The reference element has the child elements:

· interface : Interface (1..1) - A reference has one interface, which describes the operations used by the reference. The interface is described by an interface element which is a child element of the reference element. For details on the interface element see the Interface section.

· binding : Binding (0..n) - A reference element has zero or more binding elements as children. Details of the binding element are described in the Bindings section.

When used with a reference element, a binding element specifies an endpoint which is the target of that binding. A reference cannot mix the use of endpoints specified via binding elements with target endpoints specified via the @target attribute. If the @target attribute is set, the reference cannot also have binding subelements. If binding elements with endpoints are specified, each endpoint uses the binding type of the binding element in which it is defined.

· callback (0..1) / binding : Binding (1..n) - al callback element is used if the interface has a callback defined and the callback element has one or more binding elements as subelements. The callback and its binding subelements are specified if there is a need to have binding details used to handle callbacks. If the callback element is not present, the behaviour is runtime implementation dependent. For details on callbacks, see the Bidirectional Interfaces section.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

For a full description of the setting of target service(s) for a reference, see the section "Specifying the Target Service(s) for a Reference".

3.1.3 Property

Properties allow for the configuration of an implementation with externally set values. Each Property is defined as a property element. The componentType element can have zero or more property elements as its children. Snippet ‎3‑4 shows the componentType pseudo-schema with the pseudo-schema for a reference child element:

<?xml version="1.0" encoding="ASCII"?>

<service … />*

<reference … >*

<property name="xs:NCName" (type="xs:QName" | element="xs:QName")

many="xs:boolean"? mustSupply="xs:boolean"?>*

default-property-value?

</property>

<implementation … />?

</componentType>

Snippet ‎3‑4: componentType Pseudo-Schema with property Child Element

The property element has the attributes:

· name : NCName (1..1) - the name of the property. The @name attribute of a <property/> child element of a <componentType/> MUST be unique amongst the property elements of that <componentType/>. [ASM40005]

· one of (1..1):

– type : QName - the type of the property defined as the qualified name of an XML schema type. The value of the property @type attribute MUST be the QName of an XML schema type. [ASM40007]

– element : QName - the type of the property defined as the qualified name of an XML schema global element – the type is the type of the global element. The value of the property @element attribute MUST be the QName of an XSD global element. [ASM40008]

A single property element MUST NOT contain both a @type attribute and an @element attribute. [ASM40010]

· many : boolean (0..1) - whether the property is single-valued (false) or multi-valued (true). In the case of a multi-valued property, it is presented to the implementation as a collection of property values. If many is not specified, it takes a default value of false.

· mustSupply : boolean (0..1) - whether the property value needs to be supplied by the component that uses the implementation. Default value is "false". When the componentType has @mustSupply="true" for a property element, a component using the implementation MUST supply a value for the property since the implementation has no default value for the property. [ASM40011] If the implementation has a default-property-value then @mustSupply="false" is appropriate, since the implication of a default value is that it is used when a value is not supplied by the using component.

· file : anyURI (0..1) - a dereferencable URI to a file containing a value for the property. The value of the property @file attribute MUST be a dereferencable URI to a file containing the value for the property. [ASM40012] The URI can be an absolute URI or a relative URI. For a relative URI, it is taken relative to the base of the contribution containing the implementation. For a description of the format of the file, see the section on Property Value File Format.

The property element can contain a default property value as its content. The form of the default property value is as described in the section on Component Property.

The value for a property is supplied to the implementation of a component at the time that the implementation is started. The implementation can use the supplied value in any way that it chooses. In particular, the implementation can alter the internal value of the property at any time. However, if the implementation queries the SCA system for the value of the property, the value as defined in the SCA composite is the value returned.

The componentType property element can contain an SCA default value for the property declared by the implementation. However, the implementation can have a property which has an implementation defined default value, where the default value is not represented in the componentType. An example of such a default value is where the default value is computed at runtime by some code contained in the implementation. If a using component needs to control the value of a property used by an implementation, the component sets the value explicitly. The SCA runtime MUST ensure that any implementation default property value is replaced by a value for that property explicitly set by a component using that implementation. [ASM40009][ Show » ]

3.1.4 Implementation

Implementation represents characteristics inherent to the implementation itself, in particular intents and policies. See the Policy Framework specification [SCA-POLICY] for a description of intents and policies. Snippet ‎3‑5 shows the componentType pseudo-schema with the pseudo-schema for a implementation child element:

<?xml version="1.0" encoding="ASCII"?>

<service … />*

<reference … >*

<property … />*

<implementation requires="list of xs:QName"?

policySets="list of xs:QName"?>

<requires/>*

<policySetAttachment/>*

</implementation>?

</componentType>

Snippet ‎3‑5: componentType Pseudo-Schema with implementation Child Element

The implementation element has the attributes:

· requires : listOfQNames (0..1) - a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets : listOfQNames (0..1) - a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The implementation element has the subelements:

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

3.2 Example ComponentType

Snippet ‎3‑6 shows the contents of the componentType file for the MyValueServiceImpl implementation. The componentType file shows the services, references, and properties of the MyValueServiceImpl implementation. In this case, Java is used to define interfaces:

<?xml version="1.0" encoding="ASCII"?>

<componentType xmlns=http://docs.oasis-open.org/ns/opencsa/sca/200912

xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<interface.java interface="services.myvalue.MyValueService"/>

</service>

<interface.java interface="services.customer.CustomerService"/>

</reference>

<interface.java

interface="services.stockquote.StockQuoteService"/>

</reference>

</componentType>

Snippet ‎3‑6: Example componentType

3.3 Example Implementation

Snippet ‎3‑7 and Snippet ‎3‑8 are an example implementation, written in Java.

AccountServiceImpl implements the AccountService interface, which is defined via a Java interface:

package services.account;

@Remotable

public interface AccountService {

AccountReport getAccountReport(String customerID);

}

Snippet ‎3‑7: Example Interface in Java

Snippet ‎3‑8 is a full listing of the AccountServiceImpl class, showing the Service it implements, plus the service references it makes and the settable properties that it has. Notice the use of Java annotations to mark SCA aspects of the code, including the @Property, @Reference and @Service annotations:

package services.account;

import java.util.List;

import commonj.sdo.DataFactory;

import org.oasisopen.sca.annotation.Property;

import org.oasisopen.sca.annotation.Reference;

import org.oasisopen.sca.annotation.Service;

import services.accountdata.AccountDataService;

import services.accountdata.CheckingAccount;

import services.accountdata.SavingsAccount;

import services.accountdata.StockAccount;

import services.stockquote.StockQuoteService;

@Service(AccountService.class)

public class AccountServiceImpl implements AccountService {

@Property

private String currency = "USD";

@Reference

private AccountDataService accountDataService;

@Reference

private StockQuoteService stockQuoteService;

public AccountReport getAccountReport(String customerID) {

DataFactory dataFactory = DataFactory.INSTANCE;

AccountReport accountReport =

(AccountReport)dataFactory.create(AccountReport.class);

List accountSummaries = accountReport.getAccountSummaries();

CheckingAccount checkingAccount = accountDataService.getCheckingAccount(customerID);

AccountSummary checkingAccountSummary =

(AccountSummary)dataFactory.create(AccountSummary.class);

checkingAccountSummary.setAccountNumber(checkingAccount.getAccountNumber());

checkingAccountSummary.setAccountType("checking");

checkingAccountSummary.setBalance(fromUSDollarToCurrency(checkingAccount.getBalance()));

accountSummaries.add(checkingAccountSummary);

SavingsAccount savingsAccount = accountDataService.getSavingsAccount(customerID);

AccountSummary savingsAccountSummary =

(AccountSummary)dataFactory.create(AccountSummary.class);

savingsAccountSummary.setAccountNumber(savingsAccount.getAccountNumber());

savingsAccountSummary.setAccountType("savings");

savingsAccountSummary.setBalance(fromUSDollarToCurrency(savingsAccount.getBalance()));

accountSummaries.add(savingsAccountSummary);

StockAccount stockAccount = accountDataService.getStockAccount(customerID);

AccountSummary stockAccountSummary =

(AccountSummary)dataFactory.create(AccountSummary.class);

stockAccountSummary.setAccountNumber(stockAccount.getAccountNumber());

stockAccountSummary.setAccountType("stock");

float balance =

(stockQuoteService.getQuote(stockAccount.getSymbol()))*stockAccount.getQuantity();

stockAccountSummary.setBalance(fromUSDollarToCurrency(balance));

accountSummaries.add(stockAccountSummary);

return accountReport;

}

private float fromUSDollarToCurrency(float value){

if (currency.equals("USD")) return value; else

if (currency.equals("EURO")) return value * 0.8f; else

return 0.0f;

}

Snippet ‎3‑8: Example Component Implementation in Java

The following is the SCA componentType definition for the AccountServiceImpl, derived by introspection of the code above:

<?xml version="1.0" encoding="ASCII"?>

<componentType xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<interface.java interface="services.account.AccountService"/>

</service>

<interface.java

interface="services.accountdata.AccountDataService"/>

</reference>

<interface.java

interface="services.stockquote.StockQuoteService"/>

</reference>

</componentType>

Snippet ‎3‑9: Example componentType for Implementation in Snippet ‎3‑8

Note that the componentType property element for "currency" has no default value declared, despite the code containing an initializer for the property field setting it to "USD". This is because the initializer cannot be introspected at runtime and the value cannot be extracted.

For full details about Java implementations, see the Java Component Implementation Specification [SCA-Java]. Other implementation types have their own specification documents.

4 Component

Components are the basic elements of business function in an SCA assembly, which are combined into complete business solutions by SCA composites.

Components are configured instances of implementations. Components provide and consume services. More than one component can use and configure the same implementation, where each component configures the implementation differently.

Components are declared as subelements of a composite in a file with a .composite extension. A component is represented by a component element which is a child of the composite element. There can be zero or more component elements within a composite. Snippet ‎4‑1 shows the composite pseudo-schema with the pseudo-schema for the component child element:

<?xml version="1.0" encoding="UTF-8"?>

…

<component name="xs:NCName" autowire="xs:boolean"?

requires="list of xs:QName"? policySets="list of xs:QName"?>*

<implementation … />?

<service … />*

<reference … />*

<property … />*

<requires/>*

<policySetAttachment/>*

</component>

…

</composite>

Snippet ‎4‑1: composite Pseudo-Schema with component Child Element

The component element has the attributes:

· name : NCName (1..1) – the name of the component. The @name attribute of a <component/> child element of a <composite/> MUST be unique amongst the component elements of that <composite/> [ASM50001]

· autowire : boolean (0..1) – whether contained component references are autowired, as described in the Autowire section. Default is false.

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The component element has the child elements:

· implementation : ComponentImplementation (0..1) – see component implementation section.

· service : ComponentService (0..n) – see component service section.

· reference : ComponentReference (0..n) – see component reference section.

· property : ComponentProperty (0..n) – see component property section.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

4.1 Implementation

A component element has one implementation element as its child, which points to the implementation used by the component.

<?xml version="1.0" encoding="UTF-8"?>

…

<component … >*

<implementation requires="list of xs:QName"?

policySets="list of xs:QName"?>

<requires/>*

<policySetAttachment/>*

</implementation>

<service … />*

<reference … />*

<property … />*

</component>

…

</composite>

Snippet ‎4‑2: component Psuedo-Schema with implementation Child Element

The component provides the extensibility point in the assembly model for different implementation types. The references to implementations of different types are expressed by implementation type specific implementation elements.

For example the elements implementation.java, implementation.bpel, implementation.cpp, and implementation.c point to Java, BPEL, C++, and C implementation types respectively. implementation.composite points to the use of an SCA composite as an implementation. implementation.spring and implementation.ejb are used for Java components written to the Spring framework and the Java EE EJB technology respectively.

Snippet ‎4‑3 – Snippet ‎4‑5 show implementation elements for the Java and BPEL implementation types and for the use of a composite as an implementation:

<implementation.java class="services.myvalue.MyValueServiceImpl"/>

Snippet ‎4‑3: Example implementation.java Element

<implementation.bpel process="ans:MoneyTransferProcess"/>

Snippet ‎4‑4: Example implementation.bpel Element

<implementation.composite name="bns:MyValueComposite"/>

Snippet ‎4‑5: Example implementation.composite Element

New implementation types can be added to the model as described in the Extension Model section.

At runtime, an implementation instance is a specific runtime instantiation of the implementation – its runtime form depends on the implementation technology used. The implementation instance derives its business logic from the implementation on which it is based, but the values for its properties and references are derived from the component which configures the implementation.

Figure ‎4‑1: Relationship of Component and Implementation

4.2 Service

The component element can have zero or more service elements as children which are used to configure the services of the component. The services that can be configured are defined by the implementation. Snippet ‎4‑6 shows the component pseudo-schema with the pseudo-schema for a service child element:

<?xml version="1.0" encoding="UTF-8"?>

…

<component … >*

<service name="xs:NCName" requires="list of xs:QName"?

policySets="list of xs:QName"?>*

<interface … />?

<binding … />*

<callback>?

<binding … />+

</callback>

<requires/>*

<policySetAttachment/>*

</service>

<reference … />*

<property … />*

</component>

…

</composite>

Snippet ‎4‑6: component Psuedo-Schema with service Child Element

The component service element has the attributes:

· name : NCName (1..1) - the name of the service. The @name attribute of a service element of a <component/> MUST be unique amongst the service elements of that <component/> [ASM50002] The @name attribute of a service element of a <component/> MUST match the @name attribute of a service element of the componentType of the <implementation/> child element of the component. [ASM50003]

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.
Note: The effective set of policy intents for the service consists of any intents explicitly stated in this @requires attribute, combined with any intents specified for the service by the implementation.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The component service element has the child elements:

· interface : Interface (0..1) - A service has zero or one interface, which describes the operations provided by the service. The interface is described by an interface element which is a child element of the service element. If no interface is specified, then the interface specified for the service in the componentType of the implementation is in effect. If an interface is declared for a component service, the interface MUST provide a compatible subset of the interface declared for the equivalent service in the componentType of the implementation [ASM50004] For details on the interface element see the Interface section.

· binding : Binding (0..n) - A service element has zero or more binding elements as children. If no binding elements are specified for the service, then the bindings specified for the equivalent service in the componentType of the implementation MUST be used, but if the componentType also has no bindings specified, then <binding.sca/> MUST be used as the binding. If binding elements are specified for the service, then those bindings MUST be used and they override any bindings specified for the equivalent service in the componentType of the implementation. [ASM50005] Details of the binding element are described in the Bindings section. The binding, combined with any PolicySets in effect for the binding, needs to satisfy the set of policy intents for the service, as described in the Policy Framework specification [SCA-POLICY].

· callback (0..1) / binding : Binding (1..n) - A callback element is used if the interface has a callback defined and the callback element has one or more binding elements as subelements. The callback and its binding subelements are specified if there is a need to have binding details used to handle callbacks. If the callback element is present and contains one or more binding child elements, then those bindings MUST be used for the callback. [ASM50006] If the callback element is not present, the behaviour is runtime implementation dependent.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

4.3 Reference

The component element can have zero or more reference elements as children which are used to configure the references of the component. The references that can be configured are defined by the implementation. Snippet ‎4‑7 shows the component pseudo-schema with the pseudo-schema for a reference child element:

<?xml version="1.0" encoding="UTF-8"?>

…

<component … >*

<service … />*

<reference name="xs:NCName"

target="list of xs:anyURI"? autowire="xs:boolean"?

multiplicity="0..1 or 1..1 or 0..n or 1..n"?

nonOverridable="xs:boolean"

wiredByImpl="xs:boolean"? requires="list of xs:QName"?

policySets="list of xs:QName"?>*

<interface … />?

<binding uri="xs:anyURI"? requires="list of xs:QName"?

policySets="list of xs:QName"?/>*

<callback>?

<binding … />+

</callback>

<requires/>*

<policySetAttachment/>*

</reference>

<property … />*

</component>

…

</composite>

Snippet ‎4‑7: component Psuedo-Schema with reference Child Element

The component reference element has the attributes:

· name : NCName (1..1) – the name of the reference. The @name attribute of a service element of a <component/> MUST be unique amongst the service elements of that <component/> [ASM50007] The @name attribute of a reference element of a <component/> MUST match the @name attribute of a reference element of the componentType of the <implementation/> child element of the component. [ASM50008]

· autowire : boolean (0..1) – whether the reference is autowired, as described in the Autowire section. The default value of the @autowire attribute MUST be the value of the @autowire attribute on the component containing the reference, if present, or else the value of the @autowire attribute of the composite containing the component, if present, and if neither is present, then it is "false". [ASM50043]

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.
Note: The effective set of policy intents for the reference consists of any intents explicitly stated in this @requires attribute, combined with any intents specified for the reference by the implementation.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· multiplicity : 0..1|1..1|0..n|1..n (0..1) - defines the number of wires that can connect the reference to target services. Overrides the multiplicity specified for this reference in the componentType of the implementation. The multiplicity can have the following values

– 0..1 – zero or one wire can have the reference as a source

– 1..1 – one wire can have the reference as a source

– 0..n - zero or more wires can have the reference as a source

– 1..n – one or more wires can have the reference as a source

The value of multiplicity for a component reference MUST only be equal or further restrict any value for the multiplicity of the reference with the same name in the componentType of the implementation, where further restriction means 0..n to 0..1 or 1..n to 1..1. [ASM50009]

If not present, the value of multiplicity is equal to the multiplicity specificed for this reference in the componentType of the implementation - if not present in the componentType, the value defaults to 1..1.

· target : anyURI (0..n) – a list of one or more of target service URI’s, depending on multiplicity setting. Each value wires the reference to a component service that resolves the reference. For more details on wiring see the section on Wires. Overrides any target specified for this reference on the implementation.

· wiredByImpl : boolean (0..1) – a boolean value, "false" by default, which indicates that the implementation wires this reference dynamically. If set to "true" it indicates that the target of the reference is set at runtime by the implementation code (e.g. by the code obtaining an endpoint reference by some means and setting this as the target of the reference through the use of programming interfaces defined by the relevant Client and Implementation specification). If @wiredByImpl="true" is set for a reference, then the reference MUST NOT be wired statically within a composite, but left unwired. [ASM50010]

· nonOverridable : boolean (0..1) - a boolean value, "false" by default, which indicates whether this component reference can have its targets overridden by a composite reference which promotes the component reference.
If @nonOverridable==false, if any target(s) are configured onto the composite references which promote the component reference, then those targets replace all the targets explicitly declared on the component reference for any value of @multiplicity on the component reference. If no targets are defined on any of the composite references which promote the component reference, then any targets explicitly declared on the component reference are used. This means in effect that any targets declared on the component reference act as default targets for that reference.

If a component reference has @multiplicity 0..1 or 1..1 and @nonOverridable==true, then the component reference MUST NOT be promoted by any composite reference. [ASM50042]

If @nonOverridable==true, and the component reference @multiplicity is 0..n or 1..n, any targets configured onto the composite references which promote the component reference are added to any references declared on the component reference - that is, the targets are additive.

The component reference element has the child elements:

· interface : Interface (0..1) - A reference has zero or one interface, which describes the operations of the reference. The interface is described by an interface element which is a child element of the reference element. If no interface is specified, then the interface specified for the reference in the componentType of the implementation is in effect. If an interface is declared for a component reference, the interface MUST provide a compatible superset of the interface declared for the equivalent reference in the componentType of the implementation. [ASM50011] For details on the interface element see the Interface section.

· binding : Binding (0..n) - A reference element has zero or more binding elements as children.If no binding elements are specified for the reference, then the bindings specified for the equivalent reference in the componentType of the implementation MUST be used. If binding elements are specified for the reference, then those bindings MUST be used and they override any bindings specified for the equivalent reference in the componentType of the implementation. [ASM50012] It is valid for there to be no binding elements on the component reference and none on the reference in the componentType - the binding used for such a reference is determined by the target service. See the section on the bindings of component services for a description of how the binding(s) applying to a service are determined.

Details of the binding element are described in the Bindings section. The binding, combined with any PolicySets in effect for the binding, needs to satisfy the set of policy intents for the reference, as described in the Policy Framework specification [SCA-POLICY].

A reference identifies zero or more target services that satisfy the reference. This can be done in a number of ways, which are fully described in section "Specifying the Target Service(s) for a Reference"

· callback (0..1) / binding : Binding (1..n) - A callback element used if the interface has a callback defined and the callback element has one or more binding elements as subelements. The callback and its binding subelements are specified if there is a need to have binding details used to handle callbacks. If the callback element is present and contains one or more binding child elements, then those bindings MUST be used for the callback. [ASM50006] If the callback element is not present, the behaviour is runtime implementation dependent.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

4.3.1 Specifying the Target Service(s) for a Reference

A reference defines zero or more target services that satisfy the reference. The target service(s) can be defined in the following ways:

1. Through a value specified in the @target attribute of the reference element

2. Through a target URI specified in the @uri attribute of a binding element which is a child of the reference element

3. Through the setting of one or more values for binding-specific attributes and/or child elements of a binding element that is a child of the reference element

4. Through the specification of @autowire="true" for the reference (or through inheritance of that value from the component or composite containing the reference)

5. Through the specification of @wiredByImpl="true" for the reference

6. Through the promotion of a component reference by a composite reference of the composite containing the component (the target service is then identified by the configuration of the composite reference)

7. Through the presence of a <wire/> element which has the reference specified in its @source attribute.

Combinations of these different methods are allowed, and the following rules MUST be observed:

· If @wiredByImpl="true", other methods of specifying the target service MUST NOT be used. [ASM50013]

· If @autowire="true", the autowire procedure MUST only be used if no target is identified by any of the other ways listed above. It is not an error if @autowire="true" and a target is also defined through some other means, however in this case the autowire procedure MUST NOT be used. [ASM50014]

· If a reference has a value specified for one or more target services in its @target attribute, there MUST NOT be any child <binding/> elements declared for that reference. [ASM50026]

· If a binding element has a value specified for a target service using its @uri attribute, the binding element MUST NOT identify target services using binding specific attributes or elements. [ASM50015]

· It is possible that a particular binding type uses more than a simple URI for the address of a target service. In cases where a reference element has a binding subelement that uses more than simple URI, the @uri attribute of the binding element MUST NOT be used to identify the target service - in this case binding specific attributes and/or child elements MUST be used. [ASM50016]

· If any <wire/> element with its @replace attribute set to "true" has a particular reference specified in its @source attribute, the value of the @target attribute for that reference MUST be ignored and MUST NOT be used to define target services for that reference. [ASM50034]

4.3.1.1 Multiplicity and the Valid Number of Target Services for a Reference

The number of target services configured for a reference are constrained by the following rules.

· A reference with multiplicity 0..1 MUST have no more than one target service defined. [ASM50039]

· A reference with multiplicity 1..1 MUST have exactly one target service defined. [ASM50040]

· A reference with multiplicity 1..n MUST have at least one target service defined. [ASM50041]

· A reference with multiplicity 0..n can have any number of target services defined.

Where it is detected that the rules for the number of target services for a reference have been violated, either at deployment or at execution time, an SCA Runtime MUST raise an error no later than when the reference is invoked by the component implementation. [ASM50022]

For example, where a composite is used as a component implementation, wires and target services cannot be added to the composite after deployment. As a result, for components which are part of the composite, both missing wires and wires with a non-existent target can be detected at deployment time through a scan of the contents of the composite.

A contrasting example is a component deployed to the SCA Domain. At the Domain level, the target of a wire, or even the wire itself, can form part of a separate deployed contribution and as a result these can be deployed after the original component is deployed. For the cases where it is valid for the reference to have no target service specified, the component implementation language specification needs to define the programming model for interacting with an untargetted reference.

Where a component reference is promoted by a composite reference, the promotion MUST be treated from a multiplicity perspective as providing 0 or more target services for the component reference, depending upon the further configuration of the composite reference. These target services are in addition to any target services identified on the component reference itself, subject to the rules relating to multiplicity. [ASM50025]

4.4 Property

The component element has zero or more property elements as its children, which are used to configure data values of properties of the implementation. Each property element provides a value for the named property, which is passed to the implementation. The properties that can be configured and their types are defined by the component type of the implementation. An implementation can declare a property as multi-valued, in which case, multiple property values can be present for a given property.

The property value can be specified in one of five ways:

· As a value, supplied in the @value attribute of the property element.

If the @value attribute of a component property element is declared, the type of the property MUST be an XML Schema simple type and the @value attribute MUST contain a single value of that type. [ASM50027]

For example,

Snippet ‎4‑8: Example property using @value attribute

· As a value, supplied as the content of the value subelement(s) of the property element.

If the value subelement of a component property is specified, the type of the property MUST be an XML Schema simple type or an XML schema complex type. [ASM50028]

For example,

– property defined using a XML Schema simple type and which contains a single value

</property>

Snippet ‎4‑9: Example property with a Simple Type Containing a Single Value

– property defined using a XML Schema simple type and which contains multiple values

<value>USDollar</value>

</property>

Snippet ‎4‑10: Example property with a Simple Type Containing Multiple Values

– property defined using a XML Schema complex type and which contains a single value

<foo:a>TheValue</foo:a>

<foo:b>InterestingURI</foo:b>

</value>

</property>

Snippet ‎4‑11: Example property with a Complex Type Containing a Single Value

– property defined using a XML Schema complex type and which contains multiple values

<bar:a>AValue</bar:a>

<bar:b>InterestingURI</bar:b>

</value>

<bar:a>BValue</bar:a>

<bar:b>BoringURI</bar:b>

</value>

</property>

Snippet ‎4‑12: Example property with a Complex Type Containing Multiple Values

· As a value, supplied as the content of the property element.

If a component property value is declared using a child element of the <property/> element, the type of the property MUST be an XML Schema global element and the declared child element MUST be an instance of that global element. [ASM50029]

For example,

– property defined using a XML Schema global element declartion and which contains a single value

<foo:SomeGED ...>...</foo:SomeGED>

</property>

Snippet ‎4‑13: Example property with a Global Element Declaration Containing a Single Value

– property defined using a XML Schema global element declaration and which contains multiple values

<bar:SomeOtherGED ...>...</bar:SomeOtherGED>

</property>

Snippet ‎4‑14 Example property with a Global Element Declaration Containing Multiple Values

· By referencing a Property value of the composite which contains the component. The reference is made using the @source attribute of the property element.

The form of the value of the @source attribute follows the form of an XPath expression. This form allows a specific property of the composite to be addressed by name. Where the composite property is of a complex type, the XPath expression can be extended to refer to a sub-part of the complex property value.

So, for example, source="$currency" is used to reference a property of the composite called "currency", while source="$currency/a" references the sub-part "a" of the complex composite property with the name "currency".

· By specifying a dereferencable URI to a file containing the property value through the @file attribute. The contents of the referenced file are used as the value of the property.

If more than one property value specification is present, the @source attribute takes precedence, then the @file attribute.

For a property defined using a XML Schema simple type and for which a single value is desired, can be set either using the @value attribute or the <value> child element. The two forms in such a case are equivalent.

When a property has multiple values set, all the values MUST be contained within a single property element. [ASM50044]

The type of the property can be specified in one of two ways:

· by the qualified name of a type defined in an XML schema, using the @type attribute

· by the qualified name of a global element in an XML schema, using the @element attribute

The property type specified for the property element of a component MUST be compatible with the type of the property with the same @name declared in the component type of the implementation used by the component. If no type is declared in the component property element, the type of the property declared in the componentType of the implementation MUST be used. [ASM50036]

The meaning of "compatible" for property types is defined in the section Property Type Compatibility.

Snippet ‎4‑15 shows the component pseudo-schema with the pseudo-schema for a property child element:

<?xml version="1.0" encoding="UTF-8"?>

…

<component … >*

<implementation … />?

<service … />*

<reference … />*

<property name="xs:NCName"

(type="xs:QName" | element="xs:QName")?

many="xs:boolean"?

source="xs:string"? file="xs:anyURI"?

value="xs:string"?>*

[<value>+ | xs:any+ ]?

</property>

</component>

…

</composite>

Snippet ‎4‑15: component Psuedo-Schema with property Child Element

The component property element has the attributes:

· name : NCName (1..1) – the name of the property. The @name attribute of a property element of a <component/> MUST be unique amongst the property elements of that <component/>. [ASM50031] The @name attribute of a property element of a <component/> MUST match the @name attribute of a property element of the componentType of the <implementation/> child element of the component. [ASM50037]

· zero or one of (0..1):

– type : QName – the type of the property defined as the qualified name of an XML schema type

– element : QName – the type of the property defined as the qualified name of an XML schema global element – the type is the type of the global element

A single property element MUST NOT contain both a @type attribute and an @element attribute. [ASM50035]

· source : string (0..1) – an XPath expression pointing to a property of the containing composite from which the value of this component property is obtained.

· file : anyURI (0..1) – a dereferencable URI to a file containing a value for the property. The value of the component property @file attribute MUST be a dereferencable URI to a file containing the value for the property. [ASM50045] The URI can be an absolute URI or a relative URI. For a relative URI, it is taken relative to the base of the contribution containing the composite in which the component is declared. For a description of the format of the file, see the section on Property Value File Format.

· many : boolean (0..1) – whether the property is single-valued (false) or multi-valued (true). Overrides the many specified for this property in the componentType of the implementation. The value can only be equal or further restrict, i.e. if the implementation specifies many true, then the component can say false. In the case of a multi-valued property, it is presented to the implementation as a Collection of property values. If many is not specified, it takes the value defined by the component type of the implementation used by the component.

· value : string (0..1) - the value of the property if the property is defined using a simple type.

The component property element has the child element:

· value :any (0..n) - A property has zero or more, value elements that specify the value(s) of a property that is defined using a XML Schema type. If a property is single-valued, the <value/> subelement MUST NOT occur more than once. [ASM50032] A property <value/> subelement MUST NOT be used when the @value attribute is used to specify the value for that property. [ASM50033]

4.4.1 Property Type Compatibility

There are a number of situations where the declared type of a property element is matched with the declared type of another property element. These situations include:

· Where a component <property/> sets a value for a property of an implementation, as declared in the componentType of the implementation

· Where a component <property/> gets its value from the value of a composite <property/> by means of its @source attribute. This situation can also involve the @source attribute referencing a subelement of the composite <property/> value, in which case it is the type of the subelement which must be matched with the type of the component <property/>

· Where the componentType of a composite used as an implementation is calculated and componentType <property/> elements are created for each composite <property/>

In these cases where the types of two property elements are matched, the types declared for the two <property/> elements MUST be compatible [ASM50038]

Two property types are compatible if they have the same XSD type (where declared as XSD types) or the same XSD global element (where declared as XSD global elements). For cases where the type of a property is declared using a different type system (eg Java), then the type of the property is mapped to XSD using the mapping rules defined by the appropriate implementation type specification

4.4.2 Property Value File Format

The format of the file which is referenced by the @file attribute of a component property or a componentType property is that it is an XML document which MUST contain an sca:values element which in turn contains one of:

• a set of one or more <sca:value/> elements each containing a simple string - where the property type is a simple XML type

• a set of one or more <sca:value/> elements or a set of one or more global elements - where the property type is a complex XML type

[ASM50046]

<?xml version="1.0" encoding="UTF-8"?>

<value>MyValue</value>

</values>

Snippet ‎4‑16: Property Value File Content for simple property type

<?xml version="1.0" encoding="UTF-8"?>

<foo:fooElement>

<foo:a>AValue</foo:a>

<foo:b>InterestingURI</foo:b>

</foo:fooElement>

</values/>

Snippet ‎4‑17: Property Value File Content for a complex property type

4.5 Example Component

Figure ‎4‑2 shows the component symbol that is used to represent a component in an assembly diagram.

Figure ‎4‑2: Component symbol

Figure ‎4‑3 shows the assembly diagram for the MyValueComposite containing the MyValueServiceComponent.

Figure ‎4‑3: Assembly diagram for MyValueComposite

Snippet ‎4‑18: Example composite shows the MyValueComposite.composite file for the MyValueComposite containing the component element for the MyValueServiceComponent. A value is set for the property named currency, and the customerService and stockQuoteService references are promoted:

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

name="MyValueComposite" >

<implementation.java

class="services.myvalue.MyValueServiceImpl"/>

</component>

<reference name="CustomerService"

promote="MyValueServiceComponent/customerService"/>

<reference name="StockQuoteService"

promote="MyValueServiceComponent/stockQuoteService"/>

</composite>

Snippet ‎4‑18: Example composite

Note that the references of MyValueServiceComponent are explicitly declared only for purposes of clarity – the references are defined by the MyValueServiceImpl implementation and there is no need to redeclare them on the component unless the intention is to wire them or to override some aspect of them.

The following snippet gives an example of the layout of a composite file if both the currency property and the customerService reference of the MyValueServiceComponent are declared to be multi-valued (many=true for the property and multiplicity=0..n or 1..n for the reference):

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

name="MyValueComposite" >

<implementation.java

class="services.myvalue.MyValueServiceImpl"/>

<value>USDollar</value>

</property>

<reference name="customerService"

target="InternalCustomer/customerService"/>

</component>

...

<reference name="CustomerService"

promote="MyValueServiceComponent/customerService"/>

<reference name="StockQuoteService"

promote="MyValueServiceComponent/stockQuoteService"/>

</composite>

Snippet ‎4‑19: Example composite with Multi-Valued property and reference

….this assumes that the composite has another component called InternalCustomer (not shown) which has a service to which the customerService reference of the MyValueServiceComponent is wired as well as being promoted externally through the composite reference CustomerService.

5 Composite

An SCA composite is used to assemble SCA elements in logical groupings. It is the basic unit of composition within an SCA Domain. An SCA composite contains a set of components, services, references and the wires that interconnect them, plus a set of properties which can be used to configure components.

Composites can be used as component implementations in higher-level composites – in other words the higher-level composites can have components that are implemented by composites. For more detail on the use of composites as component implementations see the section Using Composites as Component Implementations.

The content of a composite can be used within another composite through inclusion. When a composite is included by another composite, all of its contents are made available for use within the including composite – the contents are fully visible and can be referenced by other elements within the including composite. For more detail on the inclusion of one composite into another see the section Using Composites through Inclusion.

A composite can be used as a unit of deployment. When used in this way, composites contribute components and wires to an SCA Domain. A composite can be deployed to the SCA Domain either by inclusion or a composite can be deployed to the Domain as an implementation. For more detail on the deployment of composites, see the section dealing with the SCA Domain.

A composite is defined in an xxx.composite file. A composite is represented by a composite element. Snippet ‎5‑1 shows the pseudo-schema for the composite element:

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="xs:anyURI"

name="xs:NCName" local="xs:boolean"?

autowire="xs:boolean"?

requires="list of xs:QName"? policySets="list of xs:QName"?>

<include … />*

<requires/>*

<policySetAttachment/>*

<service … />*

<reference … />*

<property … />*

<component … />*

<wire … />*

</composite>

Snippet ‎5‑1: composite Pseduo-Schema

The composite element has the attributes:

· name : NCName (1..1) – the name of the composite. The form of a composite name is an XML QName, in the namespace identified by the @targetNamespace attribute. A composite @name attribute value MUST be unique within the namespace of the composite. [ASM60001]

· targetNamespace : anyURI (1..1) – an identifier for a target namespace into which the composite is declared

· local : boolean (0..1) – whether all the components within the composite all run in the same operating system process. @local="true" for a composite means that all the components within the composite MUST run in the same operating system process. [ASM60002] local="false", which is the default, means that different components within the composite can run in different operating system processes and they can even run on different nodes on a network.

· autowire : boolean (0..1) – whether contained component references are autowired, as described in the Autowire section. Default is false.

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The composite element has the child elements:

· service : CompositeService (0..n) – see composite service section.

· reference : CompositeReference (0..n) – see composite reference section.

· property : CompositeProperty (0..n) – see composite property section.

· component : Component (0..n) – see component section.

· wire : Wire (0..n) – see composite wire section.

· include : Include (0..n) – see composite include section

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

Components contain configured implementations which hold the business logic of the composite. The components offer services and use references to other services. Composite services define the public services provided by the composite, which can be accessed from outside the composite. Composite references represent dependencies which the composite has on services provided elsewhere, outside the composite. Wires describe the connections between component services and component references within the composite. Included composites contribute the elements they contain to the using composite.

Composite services involve the promotion of one service of one of the components within the composite, which means that the composite service is actually provided by one of the components within the composite. Composite references involve the promotion of one or more references of one or more components. Multiple component references can be promoted to the same composite reference, as long as each of the component references has an interface that is a compatible subset of the interface on the composite reference. Where multiple component references are promoted to the same composite reference, then they all share the same configuration, including the same target service(s).

Composite services and composite references can use the configuration of their promoted services and references respectively (such as Bindings and Policy Sets). Alternatively composite services and composite references can override some or all of the configuration of the promoted services and references, through the configuration of bindings and other aspects of the composite service or reference.

Component services and component references can be promoted to composite services and references and also be wired internally within the composite at the same time. For a reference, this only makes sense if the reference supports a multiplicity greater than 1.

5.1 Service

The services of a composite are defined by promoting services defined by components contained in the composite. A component service is promoted by means of a composite service element.

A composite service is represented by a service element which is a child of the composite element. There can be zero or more service elements in a composite. Snippet ‎5‑2 shows the composite pseudo-schema with the pseudo-schema for a service child element:

<?xml version="1.0" encoding="ASCII"?>

…

<service name="xs:NCName" promote="xs:anyURI"

requires="list of xs:QName"? policySets="list of xs:QName"?>*

<interface … />?

<binding … />*

<callback>?

<binding … />+

</callback>

<requires/>*

<policySetAttachment/>*

</service>

…

</composite>

Snippet ‎5‑2: composite Psuedo-Schema with service Child Element

The composite service element has the attributes:

· name : NCName (1..1) – the name of the service.The name of a composite <service/> element MUST be unique across all the composite services in the composite. [ASM60003] The name of the composite service can be different from the name of the promoted component service.

· promote : anyURI (1..1) – identifies the promoted service, the value is of the form <component-name>/<service-name>. The service name can be omitted if the target component only has one service. The same component service can be promoted by more then one composite service. A composite <service/> element's @promote attribute MUST identify one of the component services within that composite. [ASM60004] <include/> processing MUST take place before the processing of the @promote attribute of a composite service is performed. [ASM60038]

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute. Specified intents add to or further qualify the required intents defined by the promoted component service.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The composite service element has the child elements, whatever is not specified is defaulted from the promoted component service.

· interface : Interface (0..1) - an interface which decribes the operations provided by the composite service. If a composite service interface is specified it MUST be the same or a compatible subset of the interface provided by the promoted component service. [ASM60005] The interface is described by zero or one interface element which is a child element of the service element. For details on the interface element see the Interface section.

· binding : Binding (0..n) - If bindings are specified they override the bindings defined for the promoted component service from the composite service perspective. The bindings defined on the component service are still in effect for local wires within the composite that target the component service. A service element has zero or more binding elements as children. Details of the binding element are described in the Bindings section. For more details on wiring see the Wiring section.

· callback (0..1) / binding : Binding (1..n) - A callback element is used if the interface has a callback defined and the callback has one or more binding elements as subelements. The callback and its binding subelements are specified if there is a need to have binding details used to handle callbacks. Callback binding elements attached to the composite service override any callback binding elements defined on the promoted component service. If the callback element is not present on the composite service, any callback binding elements on the promoted service are used. If the callback element is not present at all, the behaviour is runtime implementation dependent.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

5.1.1 Service Examples

Figure ‎5‑1 shows the service symbol that used to represent a service in an assembly diagram:

Figure ‎5‑1: Service symbol

Figure ‎5‑2 shows the assembly diagram for the MyValueComposite containing the service MyValueService.

Figure ‎5‑2: MyValueComposite showing Service

Snippet ‎5‑3 shows the MyValueComposite.composite file for the MyValueComposite containing the service element for the MyValueService, which is a promote of the service offered by the MyValueServiceComponent. The name of the promoted service is omitted since MyValueServiceComponent offers only one service. The composite service MyValueService is bound using a Web service binding.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

name="MyValueComposite" >

...

<interface.java interface="services.myvalue.MyValueService"/>

<binding.ws wsdlElement="http://www.myvalue.org/MyValueService#

wsdl.port(MyValueService/MyValueServiceSOAP)"/>

</service>

<implementation.java

class="services.myvalue.MyValueServiceImpl"/>

</component>

...

</composite>

Snippet ‎5‑3: Example composite with a service

5.2 Reference

The references of a composite are defined by promoting references defined by components contained in the composite. Each promoted reference indicates that the component reference needs to be resolved by services outside the composite. A component reference is promoted using a composite reference element.

A composite reference is represented by a reference element which is a child of a composite element. There can be zero or more reference elements in a composite. Snippet ‎5‑4 shows the composite pseudo-schema with the pseudo-schema for a reference element:

<?xml version="1.0" encoding="ASCII"?>

…

<reference name="xs:NCName" target="list of xs:anyURI"?

promote="list of xs:anyURI" wiredByImpl="xs:boolean"?

multiplicity="0..1 or 1..1 or 0..n or 1..n"

requires="list of xs:QName"? policySets="list of xs:QName"?>*

<interface … />?

<binding … />*

<callback>?

<binding … />+

</callback>

<requires/>*

<policySetAttachment/>*

</reference>

…

</composite>

Snippet ‎5‑4: composite Psuedo-Schema with reference Child Element

The composite reference element has the attributes:

· name : NCName (1..1) – the name of the reference. The name of a composite <reference/> element MUST be unique across all the composite references in the composite. [ASM60006] The name of the composite reference can be different than the name of the promoted component reference.

· promote : anyURI (1..n) – identifies one or more promoted component references. The value is a list of values of the form <component-name>/<reference-name> separated by spaces. The reference name can be omitted if the component has only one reference. Each of the URIs declared by a composite reference's @promote attribute MUST identify a component reference within the composite. [ASM60007] <include/> processing MUST take place before the processing of the @promote attribute of a composite reference is performed. [ASM60037]

The same component reference can be promoted more than once, using different composite references, but only if the multiplicity defined on the component reference is 0..n or 1..n. The multiplicity on the composite reference can restrict accordingly.

Where a composite reference promotes two or more component references:

– the interfaces of the component references promoted by a composite reference MUST be the same, or if the composite reference itself declares an interface then each of the component reference interfaces MUST be a compatible subset of the composite reference interface.. [ASM60008]

– the intents declared on a composite reference and on the component references which it promoites MUST NOT be mutually exclusive. [ASM60009] The intents which apply to the composite reference in this case are the union of the intents specified for each of the promoted component references plus any intents declared on the composite reference itself. If any intents in the set which apply to a composite reference are mutually exclusive then the SCA runtime MUST raise an error. [ASM60010]

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute. Specified intents add to or further qualify the intents defined for the promoted component reference.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· multiplicity : (1..1) - Defines the number of wires that can connect the reference to target services. The multiplicity of a composite reference is always specified explicitly and can have one of the following values

– 0..1 – zero or one wire can have the reference as a source

– 1..1 – one wire can have the reference as a source

– 0..n - zero or more wires can have the reference as a source

– 1..n – one or more wires can have the reference as a source

The multiplicity of a composite reference MUST be equal to or further restrict the multiplicity of each of the component references that it promotes, with the exception that the multiplicity of the composite reference does not have to require a target if there is already a target on the component reference. This means that a component reference with multiplicity 1..1 and a target can be promoted by a composite reference with multiplicity 0..1, and a component reference with multiplicity 1..n and one or more targets can be promoted by a composite reference with multiplicity 0..n or 0..1. [ASM60011]

The valid values for composite reference multiplicity are shown in the following tables:

Composite Reference multiplicity	Component Reference multiplicity (where there are no targets declared)
Composite Reference multiplicity	0..1	1..1	0..n	1..n
0..1	YES	NO	YES	NO
1..1	YES	YES	YES	YES
0..n	NO	NO	YES	NO
1..n	NO	NO	YES	YES

Composite Reference multiplicity	Component Reference multiplicity (where there are targets declared)
Composite Reference multiplicity	0..1	1..1	0..n	1..n
0..1	YES	YES	YES	YES
1..1	YES	YES	YES	YES
0..n	NO	NO	YES	YES
1..n	NO	NO	YES	YES

· target : anyURI (0..n) – a list of one or more of target service URI’s, depending on multiplicity setting. Each value wires the reference to a service in a composite that uses the composite containg the reference as an implementation for one of its components. For more details on wiring see the section on Wires.

· wiredByImpl : boolean (0..1) – a boolean value. If set to "true" it indicates that the target of the reference is set at runtime by the implementation code (for example by the code obtaining an endpoint reference by some means and setting this as the target of the reference through the use of programming interfaces defined by the relevant Client and Implementation specification). If "true" is set, then the reference is not intended to be wired statically within a using composite, but left unwired.
All the component references promoted by a single composite reference MUST have the same value for @wiredByImpl. [ASM60035] If the @wiredByImpl attribute is not specified on the composite reference, the default value is "true" if all of the promoted component references have a wiredByImpl value of "true", and the default value is "false" if all the promoted component references have a wiredByImpl value of "false". If the @wiredByImpl attribute is specified, its value MUST be "true" if all of the promoted component references have a wiredByImpl value of "true", and its value MUST be "false" if all the promoted component references have a wiredByImpl value of "false". [ASM60036]

The composite reference element has the child elements, whatever is not specified is defaulted from the promoted component reference(s).

· interface : Interface (0..1) - zero or one interface element which declares an interface for the composite reference. If a composite reference has an interface specified, it MUST provide an interface which is the same or which is a compatible superset of the interface(s) declared by the promoted component reference(s). [ASM60012] If no interface is declared on a composite reference, the interface from one of its promoted component references MUST be used for the component type associated with the composite. [ASM60013] For details on the interface element see the Interface section.

· binding : Binding (0..n) - A reference element has zero or more binding elements as children. If one or more bindings are specified they override any and all of the bindings defined for the promoted component reference from the composite reference perspective. The bindings defined on the component reference are still in effect for local wires within the composite that have the component reference as their source. Details of the binding element are described in the Bindings section. For more details on wiring see the section on Wires.

A reference identifies zero or more target services which satisfy the reference. This can be done in a number of ways, which are fully described in section "Specifying the Target Service(s) for a Reference".

· callback (0..1) / binding : Binding (1..n) - A callback element is used if the interface has a callback defined and the callback element has one or more binding elements as subelements. The callback and its binding subelements are specified if there is a need to have binding details used to handle callbacks. Callback binding elements attached to the composite reference override any callback binding elements defined on any of the promoted component references. If the callback element is not present on the composite service, any callback binding elements that are declared on all the promoted references are used. If the callback element is not present at all, the behaviour is runtime implementation dependent.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

5.2.1 Example Reference

Figure ‎5‑3 shows the reference symbol that is used to represent a reference in an assembly diagram.

Figure ‎5‑3: Reference symbol

Figure ‎5‑4 shows the assembly diagram for the MyValueComposite containing the reference CustomerService and the reference StockQuoteService.

Figure ‎5‑4: MyValueComposite showing References

Snippet ‎5‑5 shows the MyValueComposite.composite file for the MyValueComposite containing the reference elements for the CustomerService and the StockQuoteService. The reference CustomerService is bound using the SCA binding. The reference StockQuoteService is bound using the Web service binding. The endpoint addresses of the bindings can be specified, for example using the binding @uri attribute (for details see the Bindings section), or overridden in an enclosing composite. Although in this case the reference StockQuoteService is bound to a Web service, its interface is defined by a Java interface, which was created from the WSDL portType of the target web service.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

name="MyValueComposite" >

...

<implementation.java

class="services.myvalue.MyValueServiceImpl"/>

</component>

<reference name="CustomerService"

promote="MyValueServiceComponent/customerService">

<interface.java interface="services.customer.CustomerService"/>

<binding.sca/>

</reference>

<reference name="StockQuoteService"

promote="MyValueServiceComponent/stockQuoteService">

<interface.java

interface="services.stockquote.StockQuoteService"/>

<binding.ws wsdlElement="http://www.stockquote.org/StockQuoteService#

wsdl.port(StockQuoteService/StockQuoteServiceSOAP)"/>

</reference>

...

</composite>

Snippet ‎5‑5: Example composite with a reference

5.3 Property

Properties allow for the configuration of an implementation with externally set data values. A composite can declare zero or more properties. Each property has a type, which is either simple or complex. An implementation can also define a default value for a property. Properties can be configured with values in the components that use the implementation.

Snippet ‎5‑6 shows the composite pseudo-schema with the pseudo-schema for a reference element:

<?xml version="1.0" encoding="ASCII"?>

…

<property name="xs:NCName" (type="xs:QName" | element="xs:QName")

many="xs:boolean"? mustSupply="xs:boolean"?>*

default-property-value?

</property>

…

</composite>

Snippet ‎5‑6: composite Psuedo-Schema with property Child Element

The composite property element has the attributes:

· name : NCName (1..1) - the name of the property. The @name attribute of a composite property MUST be unique amongst the properties of the same composite. [ASM60014]

· one of (1..1):

– type : QName – the type of the property - the qualified name of an XML schema type

– element : QName – the type of the property defined as the qualified name of an XML schema global element – the type is the type of the global element

A single property element MUST NOT contain both a @type attribute and an @element attribute. [ASM60040]

· many : boolean (0..1) - whether the property is single-valued (false) or multi-valued (true). The default is false. In the case of a multi-valued property, it is presented to the implementation as a collection of property values.

· mustSupply : boolean (0..1) – whether the property value has to be supplied by the component that uses the composite – when mustSupply="true" the component has to supply a value since the composite has no default value for the property. A default-property-value is only worth declaring when mustSupply="false" (the default setting for the @mustSupply attribute), since the implication of a default value is that it is used only when a value is not supplied by the using component.

The property element can contain a default-property-value, which provides default value for the property. The form of the default property value is as described in the section on Component Property.

Implementation types other than composite can declare properties in an implementation-dependent form (e.g. annotations within a Java class), or through a property declaration of exactly the form described above in a componentType file.

Property values can be configured when an implementation is used by a component. The form of the property configuration is shown in the section on Components.

5.3.1 Property Examples

For the example Property declaration and value setting in Snippet ‎5‑8, the complex type in Snippet ‎5‑7 is used as an example:

<xsd:schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://foo.com/"

xmlns:tns="http://foo.com/">

<xsd:element name="fooElement" type="tns:MyComplexType"/>

<xsd:complexType name="MyComplexType">

<xsd:sequence>

<xsd:element name="a" type="xsd:string"/>

<xsd:element name="b" type="xsd:anyURI"/>

</xsd:sequence>

</xsd:complexType>

</xsd:schema>

Snippet ‎5‑7: Complex Type for Snippet ‎5‑8

The following composite demostrates the declaration of a property of a complex type, with a default value, plus it demonstrates the setting of a property value of a complex type within a component:

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:foo="http://foo.com"

targetNamespace="http://foo.com"

name="AccountServices">

...

<value>

<foo:a>AValue</foo:a>

<foo:b>InterestingURI</foo:b>

</value>

</property>

<implementation.java class="foo.AccountServiceImpl"/>

<reference name="accountDataService"

target="AccountDataServiceComponent"/>

</component>

...

</composite>

Snippet ‎5‑8: Example property with a Complext Type

In the declaration of the property named complexFoo in the composite AccountServices, the property is defined to be of type foo:MyComplexType. The namespace foo is declared in the composite and it references the example XSD, where MyComplexType is defined. The declaration of complexFoo contains a default value. This is declared as the content of the property element. In this example, the default value consists of the element value which is of type foo:MyComplexType and it has two child elements <foo:a> and <foo:b>, following the definition of MyComplexType.

In the component AccountServiceComponent, the component sets the value of the property complexBar, declared by the implementation configured by the component. In this case, the type of complexBar is foo:MyComplexType. The example shows that the value of the complexBar property is set from the value of the complexFoo property – the @source attribute of the property element for complexBar declares that the value of the property is set from the value of a property of the containing composite. The value of the @source attribute is $complexFoo, where complexFoo is the name of a property of the composite. This value implies that the whole of the value of the source property is used to set the value of the component property.

Snippet ‎5‑9 illustrates the setting of the value of a property of a simple type (a string) from part of the value of a property of the containing composite which has a complex type:

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:foo="http://foo.com"

targetNamespace="http://foo.com"

name="AccountServices">

...

<value>

<foo:a>AValue</foo:a>

<foo:b>InterestingURI</foo:b>

</value>

</property>

<implementation.java class="foo.AccountServiceImpl"/>

<reference name="accountDataService"

target="AccountDataServiceComponent"/>

</component>

...

</composite>

Snippet ‎5‑9: Example property with a Simple Type

In the example in Snippet ‎5‑9, the component AccountServiceComponent sets the value of a property called currency, which is of type string. The value is set from a property of the composite AccountServices using the @source attribute set to $complexFoo/a. This is an XPath expression that selects the property name complexFoo and then selects the value of the a subelement of the value of complexFoo. The "a" subelement is a string, matching the type of the currency property.

Further examples of declaring properties and setting property values in a component:

– Declaration of a property with a simple type and a default value:

<value>MyValue</value>

</property>

Snippet ‎5‑10: Example property with a Simple Type and Default Value

– Declaration of a property with a complex type and a default value:

<value>

<foo:a>AValue</foo:a>

<foo:b>InterestingURI</foo:b>

</value>

</property>

Snippet ‎5‑11: Example property with a Complex Type and Default Value

– Declaration of a property with a global element type:

<foo:fooElement>

<foo:a>AValue</foo:a>

<foo:b>InterestingURI</foo:b>

</foo:fooElement>

</property>

Snippet ‎5‑12: Example property with a Global Element Type

5.4 Wire

SCA wires within a composite connect source component references to target component services.

One way of defining a wire is by configuring a reference of a component using its @target attribute. The reference element is configured with the wire-target-URI of the service(s) that resolve the reference. Multiple target services are valid when the reference has a multiplicity of 0..n or 1..n.

An alternative way of defining a Wire is by means of a wire element which is a child of the composite element. There can be zero or more wire elements in a composite. This alternative method for defining wires is useful in circumstances where separation of the wiring from the elements the wires connect helps simplify development or operational activities. An example is where the components used to build a Domain are relatively static but where new or changed applications are created regularly from those components, through the creation of new assemblies with different wiring. Deploying the wiring separately from the components allows the wiring to be created or modified with minimum effort.

Note that a Wire specified via a wire element is equivalent to a wire specified via the @target attribute of a reference. The rule which forbids mixing of wires specified with the @target attribute with the specification of endpoints in binding subelements of the reference also applies to wires specified via separate wire elements.

Snippet ‎5‑13 shows the composite pseudo-schema with the pseudo-schema for the wire child element:

...

<wire source="xs:anyURI" target="xs:anyURI" replace="xs:boolean"?/>*

...

</composite>

Snippet ‎5‑13: composite Psuedo-Schema with wire Child Element

The reference element of a component has a list of one or more of the following wire-target-URI values for the target, with multiple values separated by a space:

· <component-name>[ /<service-name> [/<binding-name>]? ]?

o <component-name> is the name of the target component.

o <service-name> is the name of the target service within the component.

If <service-name> is present, the component service with @name corresponding to <service-name> MUST be used for the wire. [ASM60046]

If there is no component service with @name corresponding to <service-name>, the SCA runtime MUST raise an error. [ASM60047]

If <service-name> is not present, the target component MUST have one and only one service with an interface that is a compatible superset of the wire source’s interface and satisifies the policy requirements of the wire source, and the SCA runtime MUST use this service for the wire. [ASM60048]

o <binding-name> is the name of the service’s binding to use. The <binding-name> can be the default name of a binding element (see section 8 “Binding”).

If <binding-name> is present, the <binding/> subelement of the target service with @name corresponding to <binding-name> MUST be used for the wire. [ASM60049] If there is no <binding/> subelement of the target service with @name corresponding to <binding-name>, the SCA runtime MUST raise an error. [ASM60050] If <binding-name> is not present and the target service has multiple <binding/> subelements, the SCA runtime MUST choose one and only one of the <binding/> elements which satisfies the mutual policy requirements of the reference and the service, and the SCA runtime MUST use this binding for the wire. [ASM60051]

The wire element has the attributes:

· source (1..1) – names the source component reference. The valid URI scheme is:

– <component-name>[/<reference-name>]?

· where the source is a component reference. The reference name can be omitted if the source component only has one reference

· target (1..1) – names the target component service. The valid URI scheme is the same as the one defined for component references above.

· replace (0..1) - a boolean value, with the default of "false". When a wire element has @replace="false", the wire is added to the set of wires which apply to the reference identified by the @source attribute. When a wire element has @replace="true", the wire is added to the set of wires which apply to the reference identified by the @source attribute - but any wires for that reference specified by means of the @target attribute of the reference are removed from the set of wires which apply to the reference.

In other words, if any <wire/> element with @replace="true" is used for a particular reference, the value of the @target attribute on the reference is ignored - and this permits existing wires on the reference to be overridden by separate configuration, where the reference is on a component at the Domain level.

<include/> processing MUST take place before the @source and @target attributes of a wire are resolved. [ASM60039]

For a composite used as a component implementation, wires can only link sources and targets that are contained in the same composite (irrespective of which file or files are used to describe the composite). Wiring to entities outside the composite is done through services and references of the composite with wiring defined by the next higher composite.

The interface declared by the target of a wire MUST be a compatible superset of the interface declared by the source of the wire. [ASM60043] See the section on Interface Compatibility for a definition of "compatible superset".

A Wire can connect between different interface languages (e.g. Java interfaces and WSDL portTypes) in either direction, as long as the operations defined by the two interface types are equivalent. They are equivalent if the operation(s), parameter(s), return value(s) and faults/exceptions map to each other.

Service clients cannot (portably) ask questions at runtime about additional interfaces that are provided by the implementation of the service (e.g. the result of “instance of” in Java is non portable). It is valid for an SCA implementation to have proxies for all wires, so that, for example, a reference object passed to an implementation might only have the business interface of the reference and might not be an instance of the (Java) class which is used to implement the target service, even where the interface is local and the target service is running in the same process.

Note: It is permitted to deploy a composite that has references that are not wired. For the case of an un-wired reference with multiplicity 1..1 or 1..n the deployment process provided by an SCA runtime SHOULD issue a warning. [ASM60021]

5.4.1 Wire Examples

Figure ‎5‑5: MyValueComposite2 showing Wires shows the assembly diagram for the MyValueComposite2 containing wires between service, components and references.

Figure ‎5‑5: MyValueComposite2 showing Wires

Snippet ‎5‑14: Example composite with a wire shows the MyValueComposite2.composite file for the MyValueComposite2 containing the configured component and service references. The service MyValueService is wired to the MyValueServiceComponent, using an explicit <wire/> element. The MyValueServiceComponent’s customerService reference is wired to the composite's CustomerService reference. The MyValueServiceComponent’s stockQuoteService reference is wired to the StockQuoteMediatorComponent, which in turn has its reference wired to the StockQuoteService reference of the composite.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

name="MyValueComposite2" >

<interface.java interface="services.myvalue.MyValueService"/>

<binding.ws wsdlElement="http://www.myvalue.org/MyValueService#

wsdl.port(MyValueService/MyValueServiceSOAP)"/>

</service>

<implementation.java

class="services.myvalue.MyValueServiceImpl"/>

</component>

<wire source="MyValueServiceComponent/stockQuoteService"

target="StockQuoteMediatorComponent"/>

<implementation.java class="services.myvalue.SQMediatorImpl"/>

</component>

<reference name="CustomerService"

promote="MyValueServiceComponent/customerService">

<interface.java interface="services.customer.CustomerService"/>

<binding.sca/>

</reference>

<reference name="StockQuoteService"

promote="StockQuoteMediatorComponent">

<interface.java

interface="services.stockquote.StockQuoteService"/>

<binding.ws wsdlElement="http://www.stockquote.org/StockQuoteService#

wsdl.port(StockQuoteService/StockQuoteServiceSOAP)"/>

</reference>

</composite>

Snippet ‎5‑14: Example composite with a wire

5.4.2 Autowire

SCA provides a feature named Autowire, which can help to simplify the assembly of composites. Autowire enables component references to be automatically wired to component services which will satisfy those references, without the need to create explicit wires between the references and the services. When the autowire feature is used, a component reference which is not promoted and which is not explicitly wired to a service within a composite is automatically wired to a target service within the same composite. Autowire works by searching within the composite for a service interface which matches the interface of the references.

The autowire feature is not used by default. Autowire is enabled by the setting of an @autowire attribute to "true". Autowire is disabled by setting of the @autowire attribute to "false" The @autowire attribute can be applied to any of the following elements within a composite:

· reference

· component

· composite

Where an element does not have an explicit setting for the @autowire attribute, it inherits the setting from its parent element. Thus a reference element inherits the setting from its containing component. A component element inherits the setting from its containing composite. Where there is no setting on any level, autowire="false" is the default.

As an example, if a composite element has autowire="true" set, this means that autowiring is enabled for all component references within that composite. In this example, autowiring can be turned off for specific components and specific references through setting autowire="false" on the components and references concerned.

For each component reference for which autowire is enabled, the SCA runtime MUST search within the composite for target services which have an interface that is a compatible superset of the interface of the reference. [ASM60022]

The intents, and policies applied to the service MUST be compatible with those on the reference when using autowire to wire a reference – so that wiring the reference to the service will not cause an error due to policy mismatch [ASM60024] (see the Policy Framework specification [SCA-POLICY] for details)

If the search finds 1 or more valid target service for a particular reference, the action taken depends on the multiplicity of the reference:

· for an autowire reference with multiplicity 0..1 or 1..1, the SCA runtime MUST wire the reference to one of the set of valid target services chosen from the set in a runtime-dependent fashion [ASM60025]

· for an autowire reference with multiplicity 0..n or 1..n, the reference MUST be wired to all of the set of valid target services [ASM60026]

If the search finds no valid target services for a particular reference, the action taken depends on the multiplicy of the reference:

· for an autowire reference with multiplicity 0..1 or 0..n, if the SCA runtime finds no valid target service, there is no problem – no services are wired and the SCA runtime MUST NOT raise an error [ASM60027]

· for an autowire reference with multiplicity 1..1 or 1..n, if the SCA runtime finds no valid target services an error MUST be raised by the SCA runtime since the reference is intended to be wired [ASM60028]

5.4.3 Autowire Examples

Snippet ‎5‑15 and Snippet ‎5‑16 demonstrate two versions of the same composite – the first version is done using explicit wires, with no autowiring used, the second version is done using autowire. In both cases the end result is the same – the same wires connect the references to the services.

Figure ‎5‑6 is a diagram for the composite:

Figure ‎5‑6: Example Composite for Autowire

Snippet ‎5‑15 is the composite using explicit wires:

<?xml version="1.0" encoding="UTF-8"?>

<composite xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"

xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:foo="http://foo.com"

targetNamespace="http://foo.com"

name="AccountComposite">

<implementation.java class="com.foo.accounts.Payments"/>

<reference name="CustomerAccountService"

target="CustomerAccountComponent"/>

<reference name="ProductPricingService"

target="ProductPricingComponent"/>

<reference name="AccountsLedgerService"

target="AccountsLedgerComponent"/>

</component>

<implementation.java class="com.foo.accounts.CustomerAccount"/>

</component>

<implementation.java class="com.foo.accounts.ProductPricing"/>

</component>

<implementation.composite name="foo:AccountsLedgerComposite"/>

</component>

<reference name="ExternalBankingService"

promote="PaymentsComponent/ExternalBankingService"/>

</composite>

Snippet ‎5‑15: Example composite with Explicit wires

Snippet ‎5‑16 is the composite using autowire:

<?xml version="1.0" encoding="UTF-8"?>

<composite xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"

xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:foo="http://foo.com"

targetNamespace="http://foo.com"

name="AccountComposite">

<interface.java class="com.foo.PaymentServiceInterface"/>

</service>

<implementation.java class="com.foo.accounts.Payments"/>

</component>

<implementation.java class="com.foo.accounts.CustomerAccount"/>

</component>

<implementation.java class="com.foo.accounts.ProductPricing"/>

</component>

<implementation.composite name="foo:AccountsLedgerComposite"/>

</component>

<reference name="ExternalBankingService"

promote="PaymentsComponent/ExternalBankingService"/>

</composite>

Snippet ‎5‑16: composite of Snippet ‎5‑15 Using autowire

In this second case, autowire is set on for the PaymentsComponent and there are no explicit wires for any of its references – the wires are created automatically through autowire.

Note: In the second example, it would be possible to omit all of the service and reference elements from the PaymentsComponent. They are left in for clarity, but if they are omitted, the component service and references still exist, since they are provided by the implementation used by the component.

5.5 Using Composites as Component Implementations

Composites can be used as component implementations in higher-level composites – in other words the higher-level composites can have components which are implemented by composites.

When a composite is used as a component implementation, it defines a boundary of visibility. Components within the composite cannot be referenced directly by the using component. The using component can only connect wires to the services and references of the used composite and set values for any properties of the composite. The internal construction of the composite is invisible to the using component. The boundary of visibility, sometimes called encapsulation, can be enforced when assembling components and composites, but such encapsulation structures might not be enforceable in a particular implementation language.

A composite used as a component implementation also needs to honor a completeness contract. The services, references and properties of the composite form a contract (represented by the component type of the composite) which is relied upon by the using component. The concept of completeness of the composite implies that, once all <include/> element processing is performed on the composite:

1. For a composite used as a component implementation, each composite service offered by the composite MUST promote a component service of a component that is within the composite. [ASM60032]

2. For a composite used as a component implementation, every component reference of components within the composite with a multiplicity of 1..1 or 1..n MUST be wired or promoted. [ASM60033] (according to the various rules for specifying target services for a component reference described in the section " Specifying the Target Service(s) for a Reference").

3. For a composite used as a component implementation, all properties of components within the composite, where the underlying component implementation specifies "mustSupply=true" for the property, MUST either specify a value for the property or source the value from a composite property. [ASM60034]

The component type of a composite is defined by the set of composite service elements, composite reference elements and composite property elements that are the children of the composite element.

Composites are used as component implementations through the use of the implementation.composite element as a child element of the component. Snippet ‎5‑17 shows the pseudo-schema for the implementation.composite element:

<implementation.composite name="xs:QName" requires="list of xs:QName"? policySets="list of xs:QName"?>

Snippet ‎5‑17: implementation.composite Pseudo-Schema

The implementation.composite element has the attributes:

· name (1..1) – the name of the composite used as an implementation. The @name attribute of an <implementation.composite/> element MUST contain the QName of a composite in the SCA Domain. [ASM60030]

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

5.5.1 Component Type of a Composite used as a Component Implementation

An SCA runtime MUST introspect the componentType of a Composite used as a Component Implementation following the rules defined in the section "Component Type of a Composite used as a Component Implementation" [ASM60045]

The componentType of a Composite used as a Component Implementation is introspected from the Composite document as follows:

A <service/> element exists for each direct <service/> subelement of the <composite/> element

@name attribute set to the value of the @name attribute of the <service/> in the composite
@requires attribute set to the value of the @requires attribute of the <service/> in the composite, if present (the value of the @requires attribute contains the intents which apply to the promoted component service, as defined in the Policy Framework specification [SCA_POLICY]). If no intents apply to the <service/> in the composite, the @requires attribute is omitted.
@policySets attribute set to the value of the @policySets attribute of the <service/> in the composite, if it is present. If the @policySets attribute of the <service/> element in the composite is absent, the @policySets attribute is omitted.
<interface/> subelement set to the <interface/> subelement of the <service/> element in the composite. If not declared on the composite service, it is set to the <interface/> subelement which applies to the component service which is promoted by the composite service (this is either an explicit <interface/> subelement of the component <service/>, or the <interface/> element of the corresponding <service/> in the componentType of the implementation used by the component).
<binding/> subelements set to the <binding/> subelements of the <service/> element in the composite. If not declared on the composite service, the <binding/> subelements which apply to the component service promoted by the composite service are used, if any are present. If none are present in both of these locations, <binding/> subelements are omitted.
<callback/> subelement is set to the <callback/> subelement of the <service/> element in the composite. If no <callback/> subelement is present on the composite <service/> element, the <callback/> subelement is omitted.

A <reference/> element exists for each direct <reference/> subelement of the <composite/> element.

@name attribute set to the value of the @name attribute of the <reference/> in the composite
@requires attribute set to the value of the @requires attribute of the <reference/> in the composite, if present (the value of the @requires attribute contains the intents which apply to the promoted component references, as defined in the Policy Framework specification [SCA_POLICY]). If no intents apply to the <reference/> in the composite, the @requires attribute is omitted.
@policySets attribute set to the value of the @policySets attribute of the <reference/> in the composite, if present. If the @policySets attribute of the <reference/> element in the composite is absent, the @policySets attribute is omitted.
@target attribute is set to the value of the @target attribute of the <reference/> in the composite, if present, otherwise the @target attribute is omitted.
@wiredByImpl attribute is set to the value of the @wiredByImpl attribute of the <reference/> in the composite, if present. If it is not declared on the composite reference, it is set to the value of the @wiredByImpl attribute of the promoted reference(s).
@multiplicity attribute is set to the value of the @multiplicity attribute of the <reference/> in the composite
<interface/> subelement set to the <interface/> subelement of the <reference/> element in the composite. If not declared on the composite reference, it is set to the <interface/> subelement which applies to one of the component reference(s) which are promoted by the composite reference (this is either an explicit <interface/> subelement of the component <reference/>, or the <interface/> element of the corresponding <reference/> in the componentType of the implementation used by the component).
<binding/> subelements set to the <binding/> subelements of the <reference/> element in the composite. Otherwise, <binding/> subelements are omitted.
<callback/> subelement is set to the <callback/> subelement of the <reference/> element in the composite. Otherwise, <callback/> subelements are omitted.

A <property/> element exists for each direct <property/> subelement of the <composite/> element.

@name attribute set to the value of the @name attribute of the <property/> in the composite
@type attribute set to the value of the @type attribute of the <property/> in the composite, if present
@element attribute set to the value of the @element attribute of the <property/> in the composite, if present
(Note: either a @type attribute is present or an @element attribute is present - one of them has to be present, but both are not allowed)
@many attribute set to the value of the @many attribute of the <property/> in the composite, if present, otherwise omitted.
@mustSupply attribute set to the value of the @mustSupply attribute of the <property/> in the composite, if present, otherwise omitted.
@requires attribute set to the value of the @requires attribute of the <property/> in the composite, if present, otherwise omitted.
@policySets attribute set to the value of the @policySets attribute of the <property/> in the composite, if present, otherwise omitted.

A <implementation/> element exists if the <composite/> element has either of the @requires or @policySets attributes declared, with:

@requires attribute set to the value of the @requires attribute of the composite, if present, otherwise omitted.
@policySets attribute set to the value of he @policySets attribute of the composite, if present, otherwise omitted.

5.5.2 Example of Composite used as a Component Implementation

Snippet ‎5‑18 shows an example of a composite which contains two components, each of which is implemented by a composite:

<?xml version="1.0" encoding="UTF-8"?>

<composite xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"

xsd:schemaLocation="http://docs.oasis-open.org/ns/opencsa/sca/200912

file:/C:/Strategy/SCA/v09_osoaschemas/schemas/sca.xsd"

xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

xmlns:foo="http://foo.com"

name="AccountComposite">

<interface.java interface="services.account.AccountService"/>

<binding.ws wsdlElement="AccountService#

wsdl.port(AccountService/AccountServiceSOAP)"/>

</service>

<reference name="stockQuoteService"

promote="AccountServiceComponent/StockQuoteService">

<interface.java

interface="services.stockquote.StockQuoteService"/>

<binding.ws

wsdlElement="http://www.quickstockquote.com/StockQuoteService#

wsdl.port(StockQuoteService/StockQuoteServiceSOAP)"/>

</reference>

<implementation.composite name="foo:AccountServiceComposite1"/>

</component>

<implementation.composite name="foo:AccountDataServiceComposite"/>

</component>

</composite>

Snippet ‎5‑18: Example of a composite Using implementation.composite

5.6 Using Composites through Inclusion

In order to assist team development, composites can be developed in the form of multiple physical artifacts that are merged into a single logical unit.

A composite can include another composite by using the include element. This provides a recursive inclusion capability. The semantics of included composites are that the element content children of the included composite are inlined, with certain modification, into the using composite. This is done recursively till the resulting composite does not contain an include element. The outer included composite element itself is discarded in this process – only its contents are included as described below:

1. All the element content children of the included composite are inlined in the including composite.

2. The attributes @targetNamespace, @name and @local of the included composites are discarded.

3. All the namespace declaration on the included composite element are added to the inlined element content children unless the namespace binding is overridden by the element content children.

4. The attribute @autowire, if specified on the included composite, is included on all inlined component element children unless the component child already specifies that attribute.

5. The attribute values of @requires and @policySet, if specified on the included composite, are merged with corresponding attribute on the inlined component, service and reference children elements. Merge in this context means a set union.

6. Extension attributes ,if present on the included composite, follow the rules defined for that extension. Authors of attribute extensions on the composite element define the rules applying to those attributes for inclusion.

If the included composite has the value true for the attribute @local then the including composite MUST have the same value for the @local attribute, else it is an error. [ASM60041]

The composite file used for inclusion can have any contents. The composite element can contain any of the elements which are valid as child elements of a composite element, namely components, services, references, wires and includes. There is no need for the content of an included composite to be complete, so that artifacts defined within the using composite or in another associated included composite file can be referenced. For example, it is permissible to have two components in one composite file while a wire specifying one component as the source and the other as the target can be defined in a second included composite file.

The SCA runtime MUST raise an error if the composite resulting from the inclusion of one composite into another is invalid. [ASM60031] For example, it is an error if there are duplicated elements in the using composite (e.g. two services with the same uri contributed by different included composites). It is not considered an erorr if the (using) composite resulting from the inclusion is incomplete (eg. wires with non-existent source or target). Such incomplete resulting composites are permitted to allow recursive composition.

Snippet ‎5‑19 snippet shows the pseudo-schema for the include element:

<?xml version="1.0" encoding="UTF-8"?>

...

<include name="xs:QName"/>*

...

</composite>

Snippet ‎5‑19: include Pseudo-Schema

The include element has the attribute:

· name: QName (1..1) – the name of the composite that is included. The @name attribute of an include element MUST be the QName of a composite in the SCA Domain. [ASM60042]

5.6.1 Included Composite Examples

Figure ‎5‑7 shows the assembly diagram for the MyValueComposite2 containing four included composites. The MyValueServices composite contains the MyValueService service. The MyValueComponents composite contains the MyValueServiceComponent and the StockQuoteMediatorComponent as well as the wire between them. The MyValueReferences composite contains the CustomerService and StockQuoteService references. The MyValueWires composite contains the wires that connect the MyValueService service to the MyValueServiceComponent, that connect the customerService reference of the MyValueServiceComponent to the CustomerService reference, and that connect the stockQuoteService reference of the StockQuoteMediatorComponent to the StockQuoteService reference. Note that this is just one possible way of building the MyValueComposite2 from a set of included composites.

Figure ‎5‑7 MyValueComposite2 built from 4 included composites

Snippet ‎5‑20 shows the contents of the MyValueComposite2.composite file for the MyValueComposite2 built using included composites. In this sample it only provides the name of the composite. The composite file itself could be used in a scenario using included composites to define components, services, references and wires.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

xmlns:foo="http://foo.com"

name="MyValueComposite2" >

</composite>

Snippet ‎5‑20: Example composite with includes

Snippet ‎5‑21 shows the content of the MyValueServices.composite file.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

xmlns:foo="http://foo.com"

name="MyValueServices" >

<interface.java interface="services.myvalue.MyValueService"/>

<binding.ws wsdlElement="http://www.myvalue.org/MyValueService#

wsdl.port(MyValueService/MyValueServiceSOAP)"/>

</service>

</composite>

Snippet ‎5‑21: Example Partial composite with Only a service

Snippet ‎5‑22 shows the content of the MyValueComponents.composite file.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

xmlns:foo="http://foo.com"

name="MyValueComponents" >

<implementation.java

class="services.myvalue.MyValueServiceImpl"/>

</component>

<implementation.java class="services.myvalue.SQMediatorImpl"/>

</component>

Snippet ‎5‑22: Example Partial composite with Only components

Snippet ‎5‑23 shows the content of the MyValueReferences.composite file.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

xmlns:foo="http://foo.com"

name="MyValueReferences" >

<reference name="CustomerService"

promote="MyValueServiceComponent/CustomerService">

<interface.java interface="services.customer.CustomerService"/>

<binding.sca/>

</reference>

<reference name="StockQuoteService"

promote="StockQuoteMediatorComponent">

<interface.java

interface="services.stockquote.StockQuoteService"/>

<binding.ws wsdlElement="http://www.stockquote.org/StockQuoteService#

wsdl.port(StockQuoteService/StockQuoteServiceSOAP)"/>

</reference>

</composite>

Snippet ‎5‑23: Example Partial composite with Only references

Snippet ‎5‑24 shows the content of the MyValueWires.composite file.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

xmlns:foo="http://foo.com"

name="MyValueWires" >

<wire source="MyValueServiceComponent/stockQuoteService"

target="StockQuoteMediatorComponent"/>

</composite>

Snippet ‎5‑24: Example Partial composite with Only a wire

5.7 Composites which Contain Component Implementations of Multiple Types

A Composite containing multiple components can have multiple component implementation types. For example, a Composite can contain one component with a Java POJO as its implementation and another component with a BPEL process as its implementation.

5.8 Structural URI of Components

The structural URI is a relative URI that describes each use of a given component in the Domain, relative to the URI of the Domain itself. It is never specified explicitly, but it calculated from the configuration of the components configured into the Domain.

A component in a composite can be used more than once in the Domain, if its containing composite is used as the implementation of more than one higher-level component. The structural URI is used to separately identify each use of a component - for example, the structural URI can be used to attach different policies to each separate use of a component.

For components directly deployed into the Domain, the structural URI is simply the name of the component.

Where components are nested within a composite which is used as the implementation of a higher level component, the structural URI consists of the name of the nested component prepended with each of the names of the components upto and including the Domain level component.

For example, consider a component named Component1 at the Domain level, where its implementation is Composite1 which in turn contains a component named Component2, which is implemented by Composite2 which contains a component named Component3. The three components in this example have the following structural URIs:

1. Component1: Component1

2. Component2: Component1/Component2

3. Component3: Component1/Component2/Component3

The structural URI can also be extended to refer to specific parts of a component, such as a service or a reference, by appending an appropriate fragment identifier to the component's structural URI, as follows:

· Service:

#service(servicename)

· Reference:

#reference(referencename)

· Service binding:

#service-binding(servicename/bindingname)

· Reference binding:

#reference-binding(referencename/bindingname)

So, for example, the structural URI of the service named "testservice" of component "Component1" is Component1#service(testservice).

6 Interface

Interfaces define one or more business functions. These business functions are provided by Services and are used by References. A Service offers the business functionality of exactly one interface for use by other components. Each interface defines one or more service operations and each operation has zero or one request (input) message and zero or one response (output) message. The request and response messages can be simple types such as a string value or they can be complex types.

SCA currently supports the following interface type systems:

· Java interfaces

· WSDL 1.1 portTypes (Web Services Definition Language [WSDL-11])

· C++ classes

· Collections of 'C' functions

SCA is also extensible in terms of interface types. Support for other interface type systems can be added through the extensibility mechanisms of SCA, as described in the Extension Model section.

Snippet ‎6‑1 shows the pseudo-schema for the interface base element:

<interface remotable="boolean"? requires="list of xs:QName"?

policySets="list of xs:QName"?>

<requires/>*

<policySetAttachment/>*

</interface>

Snippet ‎6‑1: interface Pseudo-Schema

The interface base element has the attributes:

· remotable : boolean (0..1) – indicates whether an interface is remotable or not (see the section on Local and Remotable interfaces). A value of “true” means the interface is remotable, and a value of “false” means it is not. The @remotable attribute has no default value. This attribute is used as an alternative to interface type specific mechanisms such as the @Remotable annotation on a Java interface. The remotable nature of an interface in the absence of this attribute is interface type specific. The rules governing how this attribute relates to interface type specific mechanisms are defined by each interface type. When specified on an interface definition which includes a callback, this attribute also applies to the callback interface (see the section on Bidirectional Interfaces).

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The interface element has the following subelements:

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

For information about Java interfaces, including details of SCA-specific annotations, see the SCA Java Common Annotations and APIs specification [SCA-Common-Java].

For information about WSDL interfaces, including details of SCA-specific extensions, see SCA-Specific Aspects for WSDL Interfaces and WSDL Interface Type.

For information about C++ interfaces, see the SCA C++ Client and Implementation Model specification [SCA-CPP-Client].

For information about C interfaces, see the SCA C Client and Implementation Model specification [SCA-C-Client].

6.1 Local and Remotable Interfaces

A remotable service is one which can be called by a client which is running in an operating system process different from that of the service itself (this also applies to clients running on different machines from the service). Whether a service of a component implementation is remotable is defined by the interface of the service. WSDL defined interfaces are always remotable. See the relevant specifications for details of interfaces defined using other languages.

The style of remotable interfaces is typically coarse grained and intended for loosely coupled interactions. Remotable service Interfaces MUST NOT make use of method or operation overloading. [ASM80002] This restriction on operation overloading for remotable services aligns with the WSDL 2.0 specification, which disallows operation overloading, and also with the WS-I Basic Profile 1.1 (section 4.5.3 - R2304) which has a constraint which disallows operation overloading when using WSDL 1.1.
Independent of whether the remotable service is called remotely from outside the process where the service runs or from another component running in the same process, the data exchange semantics are by-value.

Implementations of remotable services can modify input messages (parameters) during or after an invocation and can modify return messages (results) after the invocation. If a remotable service is called locally or remotely, the SCA container MUST ensure sure that no modification of input messages by the service or post-invocation modifications to return messages are seen by the caller. [ASM80003]

Snippet ‎6‑2 shows an example of a remotable java interface:

package services.hello;

@Remotable

public interface HelloService {

String hello(String message);

}

Snippet ‎6‑2: Example remotable interface

It is possible for the implementation of a remotable service to indicate that it can be called using by-reference data exchange semantics when it is called from a component in the same process. This can be used to improve performance for service invocations between components that run in the same process. This can be done using the @AllowsPassByReference annotation (see the Java Client and Implementation Specification).

A service typed by a local interface can only be called by clients that are running in the same process as the component that implements the local service. Local services cannot be published via remotable services of a containing composite. In the case of Java a local service is defined by a Java interface definition without a @Remotable annotation.

The style of local interfaces is typically fine grained and intended for tightly coupled interactions. Local service interfaces can make use of method or operation overloading.

The data exchange semantic for calls to services typed by local interfaces is by-reference.

6.2 Interface Compatibility

The compatibility of two interfaces is defined in this section and these definitions are used throughout this specification. Three forms of compatibility are defined:

· Compatible interfaces

· Compatible subset

· Compatible superset

Note that WSDL 1.1 message parts can point to an XML Schema element declaration or to an XML Schema types. When determining compatibility between two WSDL operations, a message part that points to an XML Schema element declaration is considered to be incompatible with a message part that points to an XML Schema type.

6.2.1 Compatible Interfaces

An interface A is Compatible with a second interface B if and only if all of points 1 through 7 in the following list apply:

1. interfaces A and B are either both remotable or else both local

2. the set of operations in interface A is the same as the set of operations in interface B

3. compatibility for individual operations of the interfaces A and B is defined as compatibility of the signature, i.e., the operation name, the input types, and the output types are the same

4. the order of the input and output types for each operation in interface A is the same as the order of the input and output types for the corresponding operation in interface B

5. the set of Faults and Exceptions expected by each operation in interface A is the same as the set of Faults and Exceptions specified by the corresponding operation in interface B

6. for checking the compatibility of 2 remotable interfaces which are in different interface languages, both are mapped to WSDL 1.1 (if not already WSDL 1.1) and compatibility checking is done between the WSDL 1.1 mapped interfaces.

For checking the compatibility of 2 local interfaces which are in different interface languages, the method of checking compatibility is defined by the specifications which define those interface types, which must define mapping rules for the 2 interface types concerned.

7. if either interface A or interface B declares a callback interface then both interface A and interface B declare callback interfaces and the callback interface declared on interface A is compatible with the callback interface declared on interface B, according to points 1 through 6 above

6.2.2 Compatible Subset

An interface A is a Compatible Subset of a second interface B if and only if all of points 1 through 7 in the following list apply:

1. interfaces A and B are either both remotable or else both local

2. the set of operations in interface A is the same as or is a subset of the set of operations in interface B

3. compatibility for individual operations of the interfaces A and B is defined as compatibility of the signature, i.e., the operation name, the input types, and the output types are the same

4. the order of the input and output types for each operation in interface A is the same as the order of the input and output types for the corresponding operation in interface B

5. the set of Faults and Exceptions expected by each operation in interface A is the same as or is a superset of the set of Faults and Exceptions specified by the corresponding operation in interface B

7. if either interface A or interface B declares a callback interface then both interface A and interface B declare callback interfaces and the callback interface declared on interface B is a compatible subset of the callback interface declared on interface A, according to points 1 through 6 above

6.2.3 Compatible Superset

An interface A is a Compatible Superset of a second interface B if and only if all of points 1 through 7 in the following list apply:

1. interfaces A and B are either both remotable or else both local

2. the set of operations in interface A is the same as or is a superset of the set of operations in interface B

3. compatibility for individual operations of the interfaces A and B is defined as compatibility of the signature, i.e., the operation name, the input types, and the output types are the same

4. the order of the input and output types for each operation in interface B is the same as the order of the input and output types for the corresponding operation in interface A

5. the set of Faults and Exceptions expected by each operation in interface A is the same as or is a subset of the set of Faults and Exceptions specified by the corresponding operation in interface B

7. if either interface A or interface B declares a callback interface then both interface A and interface B declare callback interfaces and the callback interface declared on interface B is a compatible superset of the callback interface declared on interface A, according to points 1 through 6 above

6.3 Bidirectional Interfaces

The relationship of a business service to another business service is often peer-to-peer, requiring a two-way dependency at the service level. In other words, a business service represents both a consumer of a service provided by a partner business service and a provider of a service to the partner business service. This is especially the case when the interactions are based on asynchronous messaging rather than on remote procedure calls. The notion of bidirectional interfaces is used in SCA to directly model peer-to-peer bidirectional business service relationships.

An interface element for a particular interface type system needs to allow the specification of a callback interface. If a callback interface is specified, SCA refers to the interface as a whole as a bidirectional interface.

Snippet ‎6‑3 shows the interface element defined using Java interfaces with a @callbackInterface attribute.

<interface.java interface="services.invoicing.ComputePrice"

callbackInterface="services.invoicing.InvoiceCallback"/>

Snippet ‎6‑3: Example interface with a callback

If a service is defined using a bidirectional interface element then its implementation implements the interface, and its implementation uses the callback interface to converse with the client that called the service interface.

If a reference is defined using a bidirectional interface element, the client component implementation using the reference calls the referenced service using the interface. The client MUST provide an implementation of the callback interface. [ASM80004]

Callbacks can be used for both remotable and local services. Either both interfaces of a bidirectional service MUST be remotable, or both MUST be local. A bidirectional service MUST NOT mix local and remote services. [ASM80005]

Note that an interface document such as a WSDL file or a Java interface can contain annotations that declare a callback interface for a particular interface (see the section on WSDL Interface type and the Java Common Annotations and APIs specification [SCA-Common-Java]). Whenever an interface document declaring a callback interface is used in the declaration of an <interface/> element in SCA, it MUST be treated as being bidirectional with the declared callback interface. [ASM80010] In such cases, there is no requirement for the <interface/> element to declare the callback interface explicitly.

If an <interface/> element references an interface document which declares a callback interface and also itself contains a declaration of a callback interface, the two callback interfaces MUST be compatible. [ASM80011]

See the section on Interface Compatibility for a definition of "compatible interfaces".

In a bidirectional interface, the service interface can have more than one operation defined, and the callback interface can also have more than one operation defined. SCA runtimes MUST allow an invocation of any operation on the service interface to be followed by zero, one or many invocations of any of the operations on the callback interface. [ASM80009] These callback operations can be invoked either before or after the operation on the service interface has returned a response message, if there is one.

For a given invocation of a service operation, which operations are invoked on the callback interface, when these are invoked, the number of operations invoked, and their sequence are not described by SCA. It is possible that this metadata about the bidirectional interface can be supplied through mechanisms outside SCA. For example, it might be provided as a written description attached to the callback interface.

6.4 Long-running Request-Response Operations

6.4.1 Background

A service offering one or more operations which map to a WSDL request-response pattern might be implemented in a long-running, potentially interruptible, way. Consider a BPEL process with receive and reply activities referencing the WSDL request-response operation. Between the two activities, the business process logic could be a long-running sequence of steps, including activities causing the process to be interrupted. Typical examples are steps where the process waits for another message to arrive or a specified time interval to expire, or the process performs asynchronous interactions such as service invocations bound to asynchronous protocols or user interactions. This is a common situation in business processes, and it causes the implementation of the WSDL request-response operation to run for a very long time, e.g., several months (!). In this case, it is not meaningful for any caller to remain in a synchronous wait for the response while blocking system resources or holding database locks.

Note that it is possible to model long-running interactions as a pair of two independent operations as described in the section on bidirectional interfaces. However, it is a common practice (and in fact much more convenient) to model a request-response operation and let the infrastructure deal with the asynchronous message delivery and correlation aspects instead of putting this burden on the application developer.

6.4.2 Definition of "long-running"

A request-response operation is considered long-running if the implementation does not guarantee the delivery of the response within any specified time interval. Clients invoking such request-response operations are strongly discouraged from making assumptions about when the response can be expected.

6.4.3 The asyncInvocation Intent

This specification permits a long-running request-response operation or a complete interface containing such operations to be marked using a policy intent with the name asyncInvocation. It is also possible for a service to set the asyncInvocation. intent when using an interface which is not marked with the asyncInvocation. intent. This can be useful when reusing an existing interface definition that does not contain SCA information.

6.4.4 Requirements on Bindings

In order to support a service operation which is marked with the asyncInvocation intent, it is necessary for the binding (and its associated policies) to support separate handling of the request message and the response message. Bindings which only support a synchronous style of message handling, such as a conventional HTTP binding, cannot be used to support long-running operations.

The requirements on a binding to support the asyncInvocation intent are the same as those to support services with bidirectional interfaces - namely that the binding needs to be able to treat the transmission of the request message separately from the transmission of the response message, with an arbitrarily large time interval between the two transmissions.

An example of a binding/policy combination that supports long-running request-response operations is a Web service binding used in conjunction with the WS-Addressing "wsam:NonAnonymousResponses" assertion.

6.4.5 Implementation Type Support

SCA implementation types can provide special asynchronous client-side and asynchronous server-side mappings to assist in the development of services and clients for long-running request-response operations.

6.5 SCA-Specific Aspects for WSDL Interfaces

There are a number of aspects that SCA applies to interfaces in general, such as marking them as having a callback interface. These aspects apply to the interfaces themselves, rather than their use in a specific place within SCA. There is thus a need to provide appropriate ways of marking the interface definitions themselves, which go beyond the basic facilities provided by the interface definition language.

For WSDL interfaces, there is an extension mechanism that permits additional information to be included within the WSDL document. SCA takes advantage of this extension mechanism. In order to use the SCA extension mechanism, the SCA namespace (http://docs.oasis-open.org/ns/opencsa/sca/200912) needs to be declared within the WSDL document.

First, SCA defines a global element in the SCA namespace which provides a mechanism to attach policy intents - requires. Snippet ‎6‑4 shows the definition of the requires element:

</sequence>

</complexType>

</element>

</simpleType>

Snippet ‎6‑4: requires WSDL extension definition

The requires element can be used as a subelement of the WSDL portType and operation elements. The element contains one or more intent names, as defined by the Policy Framework specification [SCA-POLICY]. Any service or reference that uses an interface marked with intents MUST implicitly add those intents to its own @requires list. [ASM80008]

SCA defines an attribute which is used to indicate that a given WSDL portType element (WSDL 1.1) has an associated callback interface. This is the @callback attribute, which applies to a WSDL portType element.
Snippet ‎6‑5 shows the definition of the @callback attribute:

Snippet ‎6‑5: callback WSDL extension definition

The value of the @callback attribute is the QName of a portType. The portType declared by the @callback attribute is the callback interface to use for the portType which is annotated by the @callback attribute.
Snippet ‎6‑6 is an example of a portType element with a @callback attribute:

</operation>

...

</portType>

Snippet ‎6‑6: Example use of @callback

6.6 WSDL Interface Type

The WSDL interface type is used to declare interfaces for services and for references, where the interface is defined in terms of a WSDL document. An interface is defined in terms of a WSDL 1.1 portType with the arguments and return of the service operations described using XML schema.

A WSDL interface is declared by an interface.wsdl element. Snippet ‎6‑7 shows the pseudo-schema for the interface.wsdl element:

<interface.wsdl interface="xs:anyURI" callbackInterface="xs:anyURI"?

remotable="xs:boolean"?

requires="listOfQNames"?

policySets="listOfQNames">

<requires/>*

<policySetAttachment/>*

</interface.wsdl>

Snippet ‎6‑7: interface.wsdl Pseudo-Schema

The interface.wsdl element has the attributes:

· interface : uri (1..1) - the URI of a WSDL portType

The interface.wsdl @interface attribute MUST reference a portType of a WSDL 1.1 document. [ASM80001]

· callbackInterface : uri (0..1) - a callback interface, which is the URI of a WSDL portType

The interface.wsdl @callbackInterface attribute, if present, MUST reference a portType of a WSDL 1.1 document. [ASM80016]

· remotable : boolean (0..1) – indicates whether the interface is remotable or not. @remotable has a default value of true. WSDL interfaces are always remotable and therefore an <interface.wsdl/> element MUST NOT contain remotable=”false”. [ASM80017]

· requires : listOfQNames (0..1) – a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets : listOfQNames (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

The form of the URI for WSDL portTypes follows the syntax described in the WSDL 1.1 Element Identifiers specification [WSDL11_Identifiers]

The interface.wsdl element has the following subelements:

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

6.6.1 Example of interface.wsdl

Snippet ‎6‑8 shows an interface defined by the WSDL portType "StockQuote" with a callback interface defined by the "StockQuoteCallback" portType.

<interface.wsdl interface=”http://www.stockquote.org/StockQuoteService#

wsdl.porttype(StockQuote)”

callbackInterface=”http://www.stockquote.org/StockQuoteService#

wsdl.porttype(StockQuoteCallback)”/>

Snippet ‎6‑8: Example interface.wsdl

7 Binding

Bindings are used by services and references. References use bindings to describe the access mechanism used to call a service (which can be a service provided by another SCA composite). Services use bindings to describe the access mechanism that clients (which can be a client from another SCA composite) have to use to call the service.

SCA supports the use of multiple different types of bindings. Examples include SCA service, Web service, stateless session EJB, database stored procedure, EIS service. SCA provides an extensibility mechanism by which an SCA runtime can add support for additional binding types. For details on how additional binding types are defined, see the section on the Extension Model.

A binding is defined by a binding element which is a child element of a service or of a reference element in a composite. Snippet ‎7‑1 shows the composite pseudo-schema with the pseudo-schema for the binding element.

<?xml version="1.0" encoding="ASCII"?>

...

<service ... >*

<interface … />?

<binding uri="xs:anyURI"? name="xs:NCName"?

requires="list of xs:QName"?

policySets="list of xs:QName"?>*

<wireFormat/>?

<operationSelector/>?

<requires/>*

<policySetAttachment/>*

</binding>

<callback>?

<binding uri="xs:anyURI"? name="xs:NCName"?

requires="list of xs:QName"?

policySets="list of xs:QName"?>+

<wireFormat/>?

<operationSelector/>?

<requires/>*

<policySetAttachment/>*

</binding>

</callback>

</service>

...

<reference ... >*

<interface … />?

<binding uri="xs:anyURI"? name="xs:NCName"?

requires="list of xs:QName"?

policySets="list of xs:QName"?>*

<wireFormat/>?

<operationSelector/>?

<requires/>*

<policySetAttachment/>*

</binding>

<callback>?

<binding uri="xs:anyURI"? name="xs:NCName"?

requires="list of xs:QName"?

policySets="list of xs:QName"?>+

<wireFormat/>?

<operationSelector/>?

<requires/>*

<policySetAttachment/>*

</binding>

</callback>

</reference>

...

</composite>

Snippet ‎7‑1: composite Pseudo-Schema with binding Child element

The element name of the binding element is architected; it is in itself a qualified name. The first qualifier is always named “binding”, and the second qualifier names the respective binding-type (e.g. binding.sca, binding.ws, binding.ejb, binding.eis).

A binding element has the attributes:

· uri (0..1) - has the semantic:

– The @uri attribute can be omitted.

– For a binding of a reference the @uri attribute defines the target URI of the reference. This MUST be either the componentName/serviceName/bindingName for a wire to an endpoint within the SCA Domain, or the accessible address of some service endpoint either inside or outside the SCA Domain (where the addressing scheme is defined by the type of the binding). [ASM90001]

– The circumstances under which the @uri attribute can be used are defined in section "Specifying the Target Service(s) for a Reference."

– For a binding of a service the @uri attribute defines the bindingURI. If present, the bindingURI can be used by the binding as described in the section "Form of the URI of a Deployed Binding".

· name (0..1) – a name for the binding instance (an NCName). The @name attribute allows distinction between multiple binding elements on a single service or reference. The default value of the @name attribute is the service or reference name. When a service or reference has multiple bindings, all non-callback bindings of the service or reference MUST have unique names, and all callback bindings of the service or reference MUST have unique names. [ASM90002] This uniqueness requirement implies that only one non-callback binding of a service or reference can have the default @name value, and only one callback binding of a service or reference can have the default @name value.

The @name also permits the binding instance to be referenced from elsewhere – particularly useful for some types of binding, which can be declared in a definitions document as a template and referenced from other binding instances, simplifying the definition of more complex binding instances (see the JMS Binding specification [SCA-JMSBINDING] for examples of this referencing).

· requires (0..1) - a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

A binding element has the child elements:

· wireFormat (0..1) - a wireFormat to apply to the data flowing using the binding. See the wireFormat section for details.

· operationSelector(0..1) - an operationSelector element that is used to match a particular message to a particular operation in the interface. See the operationSelector section for details

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

When multiple bindings exist for a service, it means that the service is available through any of the specified bindings. The technique that the SCA runtime uses to choose among available bindings is left to the implementation and it might include additional (nonstandard) configuration. Whatever technique is used needs to be documented by the runtime.

Services and References can always have their bindings overridden at the SCA Domain level, unless restricted by Intents applied to them.

If a reference has any bindings, they MUST be resolved, which means that each binding MUST include a value for the @uri attribute or MUST otherwise specify an endpoint. The reference MUST NOT be wired using other SCA mechanisms. [ASM90003] To specify constraints on the kinds of bindings that are acceptable for use with a reference, the user specifies either policy intents or policy sets.

Users can also specifically wire, not just to a component service, but to a specific binding offered by that target service. To wire to a specific binding of a target service the syntax "componentName/serviceName/bindingName" MUST be used. [ASM90004]

The following sections describe the SCA and Web service binding type in detail.

7.1 Messages containing Data not defined in the Service Interface

It is possible for a message to include information that is not defined in the interface used to define the service, for instance information can be contained in SOAP headers or as MIME attachments.

Implementation types can make this information available to component implementations in their execution context. The specifications for these implementation types describe how this information is accessed and in what form it is presented.

7.2 WireFormat

A wireFormat is the form that a data structure takes when it is transmitted using some communication binding. Another way to describe this is "the form that the data takes on the wire". A wireFormat can be specific to a given communication method, or it can be general, applying to many different communication methods. An example of a general wireFormat is XML text format.

Where a particular SCA binding can accommodate transmitting data in more than one format, the configuration of the binding can include a definition of the wireFormat to use. This is done using an <sca:wireFormat/> subelement of the <binding/> element.

Where a binding supports more than one wireFormat, the binding defines one of the wireFormats to be the default wireFormat which applies if no <wireFormat/> subelement is present.

The base sca:wireFormat element is abstract and it has no attributes and no child elements. For a particular wireFormat, an extension subtype is defined, using substitution groups, for example:

· <sca:wireFormat.xml/>
A wireFormat that transmits the data as an XML text datastructure

· <sca:wireFormat.jms/>
The "default JMS wireFormat" as described in the JMS Binding specification

Specific wireFormats can have elements that include either attributes or subelements or both.

For details about specific wireFormats, see the related SCA Binding specifications.

7.3 OperationSelector

An operationSelector is necessary for some types of transport binding where messages are transmitted across the transport without any explicit relationship between the message and the interface operation to which it relates. SOAP is an example of a protocol where the messages do contain explicit information that relates each message to the operation it targets. However, other transport bindings have messages where this relationship is not expressed in the message or in any related headers (pure JMS messages, for example). In cases where the messages arrive at a service without any explicit information that maps them to specific operations, it is necessary for the metadata attached to the service binding to contain the mapping information. The information is held in an operationSelector element which is a child element of the binding element.

The base sca:operationSelector element is abstract and it has no attributes and no child elements. For a particular operationSelector, an extension subtype is defined, using substitution groups, for example:

· <sca:operationSelector.XPath/>
An operation selector that uses XPath to filter out specific messages and target them to particular named operations.

Specific operationSelectors can have elements that include either attributes or subelements or both.

For details about specific operationSelectors, see the related SCA Binding specifications.

7.4 Form of the URI of a Deployed Binding

SCA Bindings specifications can choose to use the structural URI defined in the section "Structural URI of Components" above to derive a binding specific URI according to some Binding-related scheme. The relevant binding specification describes this.

Alternatively, <binding/> elements have a @uri attribute, which is termed a bindingURI.

If the bindingURI is specified on a given <binding/> element, the binding can use it to derive an endpoint URI relevant to the binding. The derivation is binding specific and is described by the relevant binding specification.

For binding.sca, which is described in the SCA Assembly specification, this is as follows:

· If the binding @uri attribute is specified on a reference, it identifies the target service in the SCA Domain by specifying the service's structural URI.

· If the binding @uri attribute is specified on a service, it is ignored.

7.4.1 Non-hierarchical URIs

Bindings that use non-hierarchical URI schemes (such as jms: or mailto:) can make use of the @uri attritibute, which is the complete representation of the URI for that service binding. Where the binding does not use the @uri attribute, the binding needs to offer a different mechanism for specifying the service address.

7.4.2 Determining the URI scheme of a deployed binding

One of the things that needs to be determined when building the effective URI of a deployed binding (i.e. endpoint) is the URI scheme. The process of determining the endpoint URI scheme is binding type specific.

If the binding type supports a single protocol then there is only one URI scheme associated with it. In this case, that URI scheme is used.

If the binding type supports multiple protocols, the binding type implementation determines the URI scheme by introspecting the binding configuration, which can include the policy sets associated with the binding.

A good example of a binding type that supports multiple protocols is binding.ws, which can be configured by referencing either an “abstract” WSDL element (i.e. portType or interface) or a “concrete” WSDL element (i.e. binding or port). When the binding references a portType or Interface, the protocol and therefore the URI scheme is derived from the intents/policy sets attached to the binding. When the binding references a “concrete” WSDL element, there are two cases:

1) The referenced WSDL binding element uniquely identifies a URI scheme. This is the most common case. In this case, the URI scheme is given by the protocol/transport specified in the WSDL binding element.

2) The referenced WSDL binding element doesn’t uniquely identify a URI scheme. For example, when HTTP is specified in the @transport attribute of the SOAP binding element, both “http” and “https” could be used as valid URI schemes. In this case, the URI scheme is determined by looking at the policy sets attached to the binding.

It is worth noting that an intent supported by a binding type can completely change the behavior of the binding. For example, when the intent "confidentiality/transport” is attached to an HTTP binding, SSL is turned on. This basically changes the URI scheme of the binding from “http” to “https”.

7.5 SCA Binding

Snippet Snippet ‎7‑2 shows the SCA binding element pseudo-schema.

<binding.sca uri="xs:anyURI"?

name="xs:NCName"?

requires="list of xs:QName"?

policySets="list of xs:QName"?>

<wireFormat/>?

<operationSelector/>?

<requires/>*

<policySetAttachment/>*

</binding.sca>

Snippet ‎7‑2: binding.sca pseudo-schema

A binding.sca element has the attributes:

· uri (0..1) - has the semantic:

– The @uri attribute can be omitted.

–         If a <binding.sca/> element of a component reference specifies a URI via its @uri attribute, then this provides a wire to a target service provided by another component. The form of the URI which points to the service of a component that is in the same composite as the source component is as follows:

              <component-name>/<service-name>
or
              <component-name>/<service-name>/<binding-name>

in cases where the service has multiple bindings present.

– The circumstances under which the @uri attribute can be used are defined in the section "Specifying the Target Service(s) for a Reference."

– For a binding.sca of a component service, the @uri attribute MUST NOT be present. [ASM90005]

· name (0..1) – a name for the binding instance (an NCName), as defined for the base <binding/> element type.

· requires (0..1) - a list of policy intents. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

· policySets (0..1) – a list of policy sets. See the Policy Framework specification [SCA-POLICY] for a description of this attribute.

A binding.sca element has the child elements:

· wireFormat (0..1) - a wireFormat to apply to the data flowing using the binding. binding.sca does not define any specific wireFormat elements.

· operationSelector(0..1) - an operationSelector element that is used to match a particular message to a particular operation in the interface. binding.sca does not define any specific operationSelector elements.

· requires : requires (0..n) - A service element has zero or more requires subelements. See the Policy Framework specification [SCA-POLICY] for a description of this element.

The SCA binding can be used for service interactions between references and services contained within the SCA Domain. The way in which this binding type is implemented is not defined by the SCA specification and it can be implemented in different ways by different SCA runtimes. The only requirement is that any specified qualities of service are implemented for the SCA binding type. Qualities of service for <binding.sca/> are expressed using intents and/or policy sets following the rules defined in the SCA Policy specification [SCA-POLICY].

The SCA binding type is not intended to be an interoperable binding type. For interoperability, an interoperable binding type such as the Web service binding is used.

An SCA runtime has to support the binding.sca binding type. See the section on SCA Runtime conformance.

A service definition with no binding element specified uses the SCA binding (see ASM50005 in section 4.2 on Component Service). <binding.sca/> only has to be specified explicitly in override cases, or when a set of bindings is specified on a service definition and the SCA binding needs to be one of them.

If a reference does not have a binding subelement specified, then the binding used is one of the bindings specified by the service provider, as long as the intents attached to the reference and the service are all honoured, as described in the section on Component References.

If the interface of the service or reference is local, then the local variant of the SCA binding will be used. If the interface of the service or reference is remotable, then either the local or remote variant of the SCA binding will be used depending on whether source and target are co-located or not.

If a <binding.sca/> element of a <component/> <reference/> specifies a URI via its @uri attribute, then this provides a wire to a target service provided by another component.

The form of the URI which points to the service of a component that is in the same composite as the source component is as follows:

· <domain-component-name>/<service-name>

7.5.1 Example SCA Binding

Snippet 7‑3 shows the MyValueComposite.composite file for the MyValueComposite containing the service element for the MyValueService and a reference element for the StockQuoteService. Both the service and the reference use an SCA binding. The target for the reference is left undefined in this binding and would have to be supplied by the composite in which this composite is used.

<?xml version="1.0" encoding="ASCII"?>

<composite xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="http://foo.com"

name="MyValueComposite" >

<interface.java interface="services.myvalue.MyValueService"/>

<binding.sca/>

…

</service>

…

<reference name="StockQuoteService"

promote="MyValueComponent/StockQuoteReference">

<interface.java interface="services.stockquote.StockQuoteService"/>

<binding.sca/>

</reference>

</composite>

Snippet 7‑3: Example binding.sca

7.6 Web Service Binding

SCA defines a Web services binding. This is described in a separate specification document [SCA-WSBINDING].

7.7 JMS Binding

SCA defines a JMS binding. This is described in a separate specification document [SCA-JMSBINDING].

8 SCA Definitions

There are a variety of SCA artifacts which are generally useful and which are not specific to a particular composite or a particular component. These shared artifacts include intents, policy sets, binding type definitions, implementation type definitions, and external attachment definitions.

All of these artifacts within an SCA Domain are defined in SCA contributions in files called META-INF/definitions.xml (relative to the contribution base URI). An SCA runtime MUST make available to the Domain all the artifacts contained within the definitions.xml files in the Domain. [ASM10002] An SCA runtime MUST reject a definitions.xml file that does not conform to the sca-definitions.xsd schema. [ASM10003]

Although the definitions are specified within a single SCA contribution, the definitions are visible throughout the Domain. Because of this, all of the QNames for the definitions contained in definitions.xml files MUST be unique within the Domain.. [ASM10001] The definitions.xml file contains a definitions element that conforms to the pseudo-schema shown in Snippet ‎8‑1:

<?xml version="1.0" encoding="ASCII"?>

<definitions xmlns="http://docs.oasis-open.org/ns/opencsa/sca/200912"

targetNamespace="xs:anyURI">

<sca:intent/>*

<sca:policySet/>*

<sca:bindingType/>*

<sca:implementationType/>*

<sca:externalAttachment/>*

</definitions>

Snippet ‎8‑1: definitions Pseudo-Schema

The definitions element has the attribute:

· targetNamespace (1..1) – the namespace into which the child elements of this definitions element are placed (used for artifact resolution)

The definitions element contains child elements – intent, policySet, bindingType, implementationType and externalAttachment. These elements are described elsewhere in this specification or in the SCA Policy Framework specification [SCA-POLICY].

9 Extension Model

The assembly model can be extended with support for new interface types, implementation types and binding types. The extension model is based on XML schema substitution groups. There are three XML Schema substitution group heads defined in the SCA namespace: interface, implementation and binding, for interface types, implementation types and binding types, respectively.

The SCA Client and Implementation specifications and the SCA Bindings specifications (see [1], [SCA-WSBINDING], [11]) use these XML Schema substitution groups to define some basic types of interfaces, implementations and bindings, but additional types can be defined as needed, where support for these extra ones is available from the runtime. The inteface type elements, implementation type elements, and binding type elements defined by the SCA specifications are all part of the SCA namespace ("http://docs.oasis-open.org/ns/opencsa/sca/200912"), as indicated in their respective schemas. New interface types, implementation types and binding types that are defined using this extensibility model, which are not part of these SCA specifications are defined in namespaces other than the SCA namespace.

The "." notation is used in naming elements defined by the SCA specifications ( e.g. <implementation.java … />, <interface.wsdl … />, <binding.ws … />), not as a parallel extensibility approach but as a naming convention that improves usability of the SCA assembly language.

Note: How to contribute SCA model extensions and their runtime function to an SCA runtime will be defined by a future version of the specification.

9.1 Defining an Interface Type

Snippet ‎9‑1 shows the base definition for the interface element and Interface type contained in sca-core.xsd; see sca-core.xsd for the complete schema.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912"

elementFormDefault="qualified">

...

</choice>

</complexType>

...

</schema>

Snippet ‎9‑1: interface and Interface Schema

Snippet ‎9‑2 is an example of how the base definition is extended to support Java interfaces. The snippet shows the definition of the interface.java element and the JavaInterface type contained in sca-interface-java.xsd.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912">

<element name="interface.java" type="sca:JavaInterface"

substitutionGroup="sca:interface"/>

<attribute name="interface" type="NCName"

use="required"/>

</extension>

</complexContent>

</complexType>

</schema>

Snippet ‎9‑2: Extending interface to interface.java

Snippet ‎9‑3 is an example of how the base definition can be extended by other specifications to support a new interface not defined in the SCA specifications. The snippet shows the definition of the my-interface-extension element and the my-interface-extension-type type.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://www.example.org/myextension"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:tns="http://www.example.org/myextension">

<element name="my-interface-extension"

type="tns:my-interface-extension-type"

substitutionGroup="sca:interface"/>

...

</extension>

</complexContent>

</complexType>

</schema>

Snippet ‎9‑3: Example interface extension

9.2 Defining an Implementation Type

Snippet ‎9‑4 shows the base definition for the implementation element and Implementation type contained in sca-core.xsd; see sca-core.xsdfor complete schema.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912"

elementFormDefault="qualified">

...

<element name="implementation" type="sca:Implementation"

abstract="true"/>

</choice>

<attribute name="requires" type="sca:listOfQNames"

use="optional"/>

<attribute name="policySets" type="sca:listOfQNames"

use="optional"/>

</extension>

</complexContent>

</complexType>

...

</schema>

Snippet ‎9‑4: implementation and Implementation Schema

Snippet ‎9‑5 shows how the base definition is extended to support Java implementation. The snippet shows the definition of the implementation.java element and the JavaImplementation type contained in sca-implementation-java.xsd.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912">

<element name="implementation.java" type="sca:JavaImplementation"

substitutionGroup="sca:implementation"/>

<attribute name="class" type="NCName"

use="required"/>

</extension>

</complexContent>

</complexType>

</schema>

Snippet ‎9‑5: Extending implementation to implementation.java

Snippet ‎9‑6 is an example of how the base definition can be extended by other specifications to support a new implementation type not defined in the SCA specifications. The snippet shows the definition of the my-impl-extension element and the my-impl-extension-type type.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://www.example.org/myextension"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:tns="http://www.example.org/myextension">

<element name="my-impl-extension" type="tns:my-impl-extension-type"

substitutionGroup="sca:implementation"/>

...

</extension>

</complexContent>

</complexType>

</schema>

Snippet ‎9‑6: Example implementation extension

In addition to the definition for the new implementation instance element, there needs to be an associated implementationType element which provides metadata about the new implementation type. The pseudo schema for the implementationType element is shown in Snippet ‎9‑7:

<implementationType type="xs:QName"

alwaysProvides="list of intent xs:QName"

mayProvide="list of intent xs:QName"/>

Snippet ‎9‑7: implementationType Pseudo-Schema

The implementation type has the attributes:

· type (1..1) – the type of the implementation to which this implementationType element applies. This is intended to be the QName of the implementation element for the implementation type, such as "sca:implementation.java"

· alwaysProvides (0..1) – a set of intents which the implementation type always provides. See the Policy Framework specification [SCA-POLICY] for details.

· mayProvide (0..1) – a set of intents which the implementation type provides only when the intent is attached to the implementation element. See the Policy Framework specification [SCA-POLICY] for details.

9.3 Defining a Binding Type

Snippet ‎9‑8 shows the base definition for the binding element and Binding type contained in sca-core.xsd; see sca-core.xsdfor complete schema.

<?xml version="1.0" encoding="UTF-8"?>

<schema xmlns="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://docs.oasis-open.org/ns/opencsa/sca/200912"

xmlns:sca="http://docs.oasis-open.org/ns/opencsa/sca/200912"

elementFormDefault="qualified">

...

<attribute name="requires" type="sca:listOfQNames"

use="optional"/>

<attribute name="policySets" type="sca:listOfQNames"

use="optional"/>

</complexType>

...

</schema>

Snippet ‎9‑8: binding and Binding Schema

Snippet <