Help TOC > PLCS technical description > Data Exchange Specifications (DEXs)
Data Exchange Specifications (DEXs) Date: 2010/03/17 11:20:10
Revision: 1.27

Introduction

The information model defined by ISO 10303-239ISO 10303-239 Industrial automation systems and integration — Product data representation and exchange Part 239: Application protocol: Product life cycle support, See: http://en.wikipedia.org/wiki/ISO_10303 and http://www.iso.org PLCSProduct Life Cycle Support The project developing ISO 10303-239. The name of ISO 10303-239 (published by ISO in 2005). has a scope that is wider than most applications or any single data exchange. It is, therefore, unlikely that any software will be able to support or declare compliance to the entire range of information supported by ISO 10303-239 PLCS. Moreover, it would be impractical to contract for data compliant with ISO 10303-239 PLCS without a means of specifying the scope required. "Data EXchange specifications" ("DEXs") are defined in order to constrain the full information model to the scope required. The way that DEX Schemas constitute overlapping subsets of ISO 1030-239 PLCS data model is illustrated in Figure 1.

NOTE    A DEX is similar in purpose to a STEPISO 10303 - Product data representation and exchange (abbreviation stands for "STandard for the Exchange of Product model data"). A family of standards for product data exchange. See: http://en.wikipedia.org/wiki/ISO_10303 AP Conformance Class, but supported by additional usage guidance (mainly in the Capabilities) and Reference DataReference Data is data that represents information about classes or individuals which are common to many users. Note: Reference Data provides a tailorable structured vocabulary that extends the PLCS information model with business specific semantics. to ensure consistent implementation. These additional features of DEXs ensure consistent implementation of the underlying EXPRESS information model.



Figure 1 —  DEXs illustrated as overlapping subsets of ISO 1030-239 PLCS information model

Figure 1 —  DEXs illustrated as overlapping subsets of ISO 1030-239 PLCS information model

NOTE    Not all the DEXs illustrated have been published, but drafts are available at the OASIS PLCS TC website (http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=plcs).

Definition: Data Exchange Specification - a subset of the ISO 10303-239 PLCS information model, designed to support data exchange for specific activities, providing guidance and rules for how to use and combine the selected entities and external Reference Data in that exchange. Each DEX includes a complete EXPRESS schema. This is a subset of the ISO 10303-239 schema with a derived XML Schema. Both can be used to define and validate a data exchange file. A DEX defined and managed by the OASIS PLCS TC may be referred to as a "PLCS DEX", as opposed to a "Business DEX".

The actual data (i.e. a package of data that is exchanged or shared, or a data exchange file) that is in accordance with a DEX information model is referred to as a DEX data setThe actual data (i.e. a package of data that is exchanged, or a data exchange file) that is exchanged in accordance with a DEX information model..

The DEXs are defined to support specific business processes. A DEX may support a part of, one, or several information flows (arrows) from the PLCS Activity ModelAn IDEF0 model that describes an application in terms of its processes and information flows. defined in AP239An ISO 10303 STEP Application Protocol (ISO10303-239) supporting the Product Life Cycle Support.. The PLCS DEXs can be used to:

DEXs and Capabilities

In addition to identifying a subset of the ISO 10303-239 PLCS information model, there is a requirement for guidance and rules for the consistent application and usage of different areas of that information model. This is achieved through the use of "Capabilities"A description of how EXPRESS entities are used to represent a given concept (a specific "functionality" or "capability"). It provides guidance and rules on what Entities should be used to represent a given concept, how the entities should be related, and what Reference Data should be used. As well as general guidance, a set of Templates are documented within a Capability to provide precise specifications of which Entities should be instantiated to represent identified concepts.. Each Capability describes how a particular generic business concept (such as a "part" or an "approval") should be represented using a set of PLCS entities.

NOTE    Capabilities are in development and will be included in a future release.

See Capabilities for further details.

DEXs and Templates

Within each Capability, patterns for structuring and instantiating data are provided in the form of "Templates"A Template is a precise specification of which entities (and attributes) in ISO 10303-239 PLCS should be instantiated, and which Reference Data should be used, to represent a concept providing documented functionality in a Capability. A Template defined and managed by the OASIS PLCS TC may be referred to as a "PLCS Template", as opposed to a "Business Template", which unambiguously define precisely which PLCS entities are required and how they should be populated. Each Capability defines one or more Templates and these form the building blocks of the data model that underlies each DEX. Each Template has just one parent Capability, but the Template may be used as a component of several DEXs, ensuring that the same concept is represented consistently.

Examples of Templates defined by the C001: assigning_identifiers (NB Capabilities are not documented in this release of the PLCS standard) Capability and used in all DEXs are the assigning_identification and assigning_identification_with_no_organization Templates.

See Templates for further details.

DEXs and Reference Data

The information model defined by ISO 10303-239 (PLCS) is generic. It holds no business specific terms. These business semantics are represented by extending the PLCS information model through classification with so called Reference DataReference Data is data that represents information about classes or individuals which are common to many users. Note: Reference Data provides a tailorable structured vocabulary that extends the PLCS information model with business specific semantics. (RD). Reference Data allows for the semantic specialization (or grouping of elements) of the generic information model into ClassesA Reference Data Class is Reference Data that represents a class. The class definition representing a Reference Data item (e.g. term, definition and rules), used to specialize entities of the information model, to make the use of them semantically more precise. It is sometimes called a "RDL class". that make the context as specific as required for the data in question. This provides a mechanism for adapting the generic model to the requirements of more specialized domains. The use of the Reference Data is identified within the DEXs, Templates and Capabilities. The OASIS PLCS TCThe technical committee within OASIS responsible for developing the PLCS DEXs http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=plcs. specifies a mechanism for the definition (and extension) of Reference Data Classes, and also defines a number of generic Reference Data Classes that may be specialized further by more specific Classes.

Examples of Reference Data Classes used by the C001: assigning_identifiers (NB Capabilities are not documented in this release of the PLCS standard) Template are the "Organization identification code" (urn:plcs:rdl:std:Organization identification code) and "Organization name" (urn:plcs:rdl:std:Organization name) Classes. These are used to indicate that an identifier used for an organization is, for example, a simple name or a formal identification code. If a formal identification code is indicated, more specialized Reference Data Classes may be used to specify that the code in question is, for example, a "CAGE" code or a "DUNS" code.

See Reference data for further details.

Usage of DEXs

A DEX can also be used as a standard against which software can claim conformance. Conformant software is able to read and write data according to the DEX EXPRESS and XML schemaA schema language developed by W3C, used with XML data files. See http://www.w3.org/XML/Schema. a, using the rules defined in Templates, and to interpret the OASISOrganization for the Advancement of Structured Information Standards http://www.oasis-open.org. Reference Data Classes correctly.

A DEX can also (and similarly) be used as the basis of a contractual deliverable, although, in most cases, an additional Reference Data LibraryA Reference Data Library (RDL) is a managed collection of Reference Data Classes that is specified separately to any data exchange file. (RDL) would be required in order to provide specific semantics. If the generic PLCS DEX does not cover the scope of the contract completely, a Business DEXA Business DEX is a DEX that has been defined outside the OASIS PLCS TC. It is, generally speaking, more business specific and may extend or specialize a PLCS DEX. A Business DEX is defined and managed within a specific Business Context. may be required. This is a further specialization of PLCS to operate within a more constrained Business ContextA "business context" is a context in which a specialized vocabulary is employed. This may be an individual organization, a larger business community, or a particular project (or initiative). A number of Business DEXs and Templates are identified within a given Business Context and each DEX is defined using the specialized vocabulary of its Business Context.. The context may be a project, an organization or enterprise. One or more Business DEXs may be defined within a context.

See Business DEXs for further details.

NOTE    In order to distinguish between the similar terms used for the components developed by the OASIS PLCS TC and the business specific work, the terms may be prefixed "PLCS" or "OASIS" for the standardization work, and "Business" for the business specific work. A DEX that is standardized by the OASIS PLCS TC is then referred to as a "PLCS DEX" or as an "OASIS DEX", rather than a "Business DEX".

Relationships between different DEXs

Different DEXs relate to different life cycle stages of a product. Some of the ways in which DEXs relate to each other and the kinds of data they share with each other is illustrated in Figure 2. The oval shapes represent business level data that is created or referenced by a DEX. Faults, Parts, Tasks etc. The Rectangles show the DEXs. The DEXs coloured grey indicate DEXs used to represent data in the design phase of the product life cycle, and the DEXs coloured yellow signify the DEXs used in the operational phase of the product life cycle.



Figure 2 —  How DEXs relate to each other.

Figure 2 —  How DEXs relate to each other.

The documentation of DEXs

The documentation of a DEX provides a description of its purpose, an account of the business process it supports, and usage guidance. It lists the Templates used, and which Reference Data Classes are used, and it provides an EXPRESS schema and an XML Schema that is derived from the EXPRESS that represents the ISO 10303-239 PLCS subset. Furthermore, it references the set of Capabilities that provide further usage guidance.

Each DEX is identified within the DEXlibDEXlib is the XML environment created for the development of PLCS OASIS DEXs and components. It is also used for the development of Business DEXs and components. The ongoing work in the DEXlib development environment is published on a daily basis in HTML at http://www.plcs.org/plcs/dexlib/dex_index.htm. repository by a number, an identifier and a name, e.g.

Each DEX comprises the following: