Search Web Services - searchRetrieve Operation: Binding for SRU 1.2 Version 1.0

Committee Draft 01

30 June 2008

Specification URIs:

This Version: (Authoritative)

Latest Version:  

Technical Committee:

OASIS Search Web Services TC


Ray Denenberg <>

Matthew Dovey <>


Ray Denenberg

Larry Dixson

Matthew Dovey

Janifer Gatenby

Ralph LeVan

Ashley Sanders a.sanders@MANCHESTER.AC.UK

Rob Sanderson

Related work:

This specification is related to:

·         Search Retrieve via URL (SRU)


This is a binding of the Search Web Services -  searchRetrieve operation – Abstract Protocol Definition. This binding is the specification of SRU 1.2.


This document was last revised or approved by the OASIS Search Web Services TC on the above date. The level of approval is also listed above. Check the “Latest Version” or “Latest Approved Version” location noted above for possible later revisions of this document.

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The non-normative errata page for this specification is located at


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Table of Contents

1      Introduction. 6

1.1        Terminology. 6

1.2        Normative References. 6

2      Overview and Model 7

2.1        Data model 7

2.2        Processing Model 7

2.3        Result Set Model 7

2.4        Diagnostic Model 8

3      Request Parameters. 9

3.1        Request Parameters for this Binding. 9

3.2        Relationship of Actual Parameters to Abstract Parameters. 9

3.2.1     Abstract Request Parameters. 9

3.2.2     Abstract/Actual Request Parameters. 10

3.2.3     Abstract/Excluded Request Parameters. 10

3.2.4     New Request Parameters. 10

4      Response Elements. 12

4.1.1     Actual Response Elements for this Binding. 12

4.2        Relationship of Actual Elements to Abstract Elements. 12

4.2.1     Abstract Response Elements. 12

4.2.2     Abstract/Actual Response Elements. 13

4.2.3     Abstract/Excluded Response Elements. 13

4.2.4     New Response Elements. 13

5      Parameter and Element Descriptions. 15

5.1        maximumRecords. 15

5.2        recordPacking. 15

5.3        recordSchema. 15

5.4        resultSetTTL and resultSetIdleTime. 15

5.5        Stylesheet 16

5.6        records. 16

5.7        diagnostics. 16

5.8        extraRequestData, extraResponseData, and extraRecordData. 16

5.9        echoedSearchRetrieveRequest 16

6      Response Schema for SRU 1.2. 18

6.1        Structure of the <Record> Element 18

Example. 19

7      Diagnostics. 20

7.1        Diagnostic List 20

7.2        Diagnostic Schema. 20

7.3        Diagnostic Examples. 20

7.3.1     Non-Surrogate Example. 20

7.3.2     Surrogate Example. 20

8      Extensions. 22

A.     Acknowledgements. 23

B.     SRU/CQL 2.0 Features. 24

B.1 Background. 24

B.2 Proposed Changes for SRU 2.0 and CQL 2.0. 24

B.2.1 Allow Non-XML Record Representations. 24

B.2.2 Proximity as Boolean Modifier 24

B.2.3 Proximity as Relation. 25

B.2.4 Parenthesized Terms. 25

B.2.5 Faceted Searching. 25

B.2.6 Result Set Size. 25

B.2.7 Multiple Query Types. 25

B.2.8 Eliminate the Version and Operation Parameters. 26


1      Introduction

This is a binding of the OASIS SWS (Search Web Services)  searchRetrieve operation – ABSTRACT PROTOCOL DEFINITION.

This binding is the specification of SRU  1.2.

1.1    Terminology

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119]. When these words are not capitalized in this document, they are meant in their natural language sense.

1.2    Normative References

[RFC2119]               S. Bradner, Key words for use in RFCs to Indicate Requirement Levels,, IETF RFC 2119, March 1997.

2      Overview and Model

2.1    Data model

The data model in the Abstract Protocol Model says that a  “datastore is a collection of units of data.  Such a unit is referred to as an abstract item…”. 

In this binding:

·         A datastore is referred to as a database.

·         An abstract item is referred to as an abstract record, or record.

The Abstract Protocol Model further notes that “Associated with a datastore are one or more formats that the server may apply to an abstract item, resulting in an exportable structure referred to as a response Item. .  Such a format is referred to as a response item type or item type..”

In this Binding:

·         A response item is referred to as a response record, or record.
Note that “abstract record” and “response record” are referred to as “record” when the meaning is clear from the context.

·         An item type is referred to as a record schema.

A record schema is an XML schema. All records within a response, as well as the response itself, are transferred in XML. Data is not assumed to be stored in XML; records that are not natively XML must be first transformed into XML before being transferred.

2.2    Processing Model

A client sends a searchRetrieve request to a server. The client formulates the request according to a binding that describes a particular request construction. (An example of such a binding is: Search Web Services (SWS) Auxiliary Binding for HTTP GET which describes the construction of an http URL to encode parameter values of the form ‘key=value’.)

The request includes request parameters including a query to be matched against the database at the server.  The server processes the query, creating a result set of records that match the query. 

The request also indicates the desired number of records to be included in the response and includes the identifier of a record schema for transfer of the records in the response. The entire response (including all of the response records) is packaged in the SRU 1.2 response schema.

The response includes records from the result set, diagnostic information, and a result set identifier that the client may use in a subsequent request to retrieve additional records.

2.3    Result Set Model

The result set model for SRU 1.2 is as described in the Abstract Protocol Definition, with the following additional feature:

 When a result set record becomes unavailable, if a client then requests that record, the server is expected to supply a surrogate diagnostic in place of the record. For example suppose a result set of three records is created, subsequently the record at position 2 is deleted, and the client then requests records 1 through 3. The server should supply, in order: record 1, a surrogate diagnostic for record 2, record 3.

2.4    Diagnostic Model

A server supplies diagnostics in the response as appropriate. A diagnostics is fatal' or non-fatal. A fatal diagnostic is generated when the execution of the request cannot proceed and no entries are available. For example, if the client supplied an invalid query there might be nothing that the server can do. A non-fatal diagnostic is one where processing may be affected but the server can continue. For example if a particular record is not available in the requested schema but others are, the server may return the ones that are available rather than failing the entire request.

Non-fatal diagnostics are further divided into two categories: 'surrogate' and 'non-surrogate'. Surrogate diagnostics take the place of a record (as described in the Result Set Model). Non-surrogate, non-fatal diagnostics are diagnostics saying that while some or all the entries are available, something may have gone wrong; for example the requested sorting algorithm might not be available. Or, it may be just a warning.

To summarize: A surrogate diagnostic replaces a record; a non-surrogate diagnostic refers to the response at large and is supplied in addition and external to the records.  A non-surrogate diagnostic may be fatal or non-fatal. So three combinations are possible:

·         surrogate, non-fatal diagnostic

·         non-surrogate, non-fatal diagnostic

·         non-surrogate, fatal diagnostic

(“Fatal, surrogate” is not a valid combination.)

3      Request Parameters

3.1    Request Parameters for this Binding

The following table describes actual request parameters defined in this binding. It combines those that are included from the Abstract  Protocol Definition  (table 3) and new request parameters  (table 5).





. Table 1: Summary of Request Parameters

Actual Parameter Name





The string: 'searchRetrieve'.



The string ‘1.2’.



A query expressed in CQL.



Positive integer. Default if omitted is 1.



See maximumRecords.



'string' or 'xml'. Default is 'xml'.  See recordPacking.



See recordSchema.



See resultSetTTL and resultSetIdleTime.



See stylesheet.



See  extraRequestData, extraResponseData, and extraRecordData

3.2    Relationship of Actual Parameters to Abstract Parameters

3.2.1    Abstract Request Parameters

The following table, copied from the Abstract Protocol Definition, summarizes the abstract parameters of the SWS searchResponse request. Each parameter occurs either in table 3 or table 4.

Table 2: Abstract Request Parameters

Abstract Parameter Name



e.g. 'text/html',  ‘application/atom+xml’ , ‘application/x-sru’  


The search query of the request.


The position within the result set of the first record to be returned. 


The number of items requested to be returned.


The number of the result group requested to be returned.


e.g. ‘string’, ‘jpeg’, ‘dc’, ‘iso2709’. From list provided by server.


The requested order of the result set.

3.2.2    Abstract/Actual Request Parameters

The following table lists those abstract request parameters that are realized as actual parameters in this binding. See table 1 for their descriptions



Table 3: Abstract/Actual Request Parameters

Abstract Parameter Name

Actual Parameter Name









3.2.3    Abstract/Excluded Request Parameters

The following table summarizes the abstract request parameters that are excluded from this binding, and why they are excluded.

Table 4: Abstract/Excluded Request Parameters

Abstract Parameter Name

Why Excluded


The response schema for SRU 1.2 is fixed.


request by group is not a feature of SRU 1.2.


The sort order is specified within the query.

3.2.4    New Request Parameters

The following table lists actual request parameters defined in this binding that are not defined as abstract parameters. See table 1 for their descriptions.

Table 5: New Request Parameters

Actual Parameter Name







4      Response Elements

4.1.1    Actual Response Elements for this Binding

The following table describes the top-level XML elements in the response. These correspond to the actual response elements (from tables 8 and 9).

Table 6: Summary of Actual Response Elements

Actual Element Name



Restrictions/Values/ Description



Mandatory, non-repeatable

` The string ‘1.2’.



Mandatory, non-repeatable

If the query fails this MUST be 0.



Optional, non-repeatable




Optional, non-repeatable

see resultSetTTL and resultSetIdleTime.



Optional, repeatable

See records



Optional, non-repeatable

If there are no remaining records, this field MUST be omitted.




Optional, non-repeatable

see diagnostics



Optional, non-repeatable

See  extraRequestData, extraResponseData, and extraRecordData




Optional, non-repeatable

see echoedSearch RetrieveRequest

4.2    Relationship of Actual Elements to Abstract Elements

4.2.1    Abstract Response Elements

The following table, copied from the Abstract Protocol Definition, summarizes the abstract elements of the SWS searchResponse response.

Table 7: Abstract Response Elements

Abstract Element Name



The number of items matched by the query.


The number of result groups in the result set.


The identifier for a result set created through the execution of the query. 


An individual response item (one of possibly many).


The next position within the result set following the final returned item.


The next result group following the group being returned.


Error message and/or diagnostics.


The server may echo the request back to the client.

4.2.2    Abstract/Actual Response Elements

The following table lists those abstract response elements that are realized as actual elements in this binding. See table 6 for their descriptions.

Table 8: Abstract/Actual Response Elements

Abstract Element Name

Actual Element Name













4.2.3    Abstract/Excluded Response Elements

The following table summarizes the abstract response elements that are excluded from this binding, and why they are excluded.

Table 4: Abstract/Excluded Response Elements

Abstract Element Name

Why Excluded


request by group is not a feature of SRU 1.2.


request by group is not a feature of SRU 1.2.

4.2.4    New Response Elements

The following table summarizes actual response elements defined in this binding that are not defined as abstract elements. See table 9 for their descriptions.

Table 9: New Response Elements

Actual Element Name




5       Parameter and Element Descriptions

5.1    maximumRecords

The request parameter maximumRecords is a non-negative integer. It may be omitted; if so the server determines the default value. The server may return less than this number of records, for example if there are fewer matching records than requested, but MUST NOT return more.

5.2    recordPacking

In order that records which are not well formed do not break the entire message, it is possible to request that they be transferred as a single string with the <, > and & characters escaped to their entity forms. Moreover some toolkits may not be able to distinguish record XML from the XML that forms the response. However, some clients may prefer that the records be transferred as XML in order to manipulate them directly with a stylesheet that renders the records and potentially also the user interface.

This distinction is made via the recordPacking parameter in the request. If the value of the parameter is 'string', then the server should escape the record before transferring it. If the value is 'xml', then it should embed the XML directly into the response. Either way, the data is transferred within the 'recordData' field. If the server cannot comply with this packing request, then it MUST return a diagnostic.

5.3    recordSchema

The requestParameter recordSchema is the XML schema of the records to be supplied in the response. The value of the parameter is the short name that the server assigns to the identifier for the schema, as listed in the server’s explain file. The default value if not supplied is determined by the server.

For example, for the  MODS Schema Version 3.3  the identifier is info:srw/schema/1/mods-v3.3, as shown in the table  at and the short name might (but need not) be ‘mods’.   (Note: schema identifiers are not restricted to those in this table.)

The server MUST supply records in the requested schema only. If the schema is unknown or a record cannot be rendered in that schema, then the server MUST return a diagnostic:

5.4    resultSetTTL and resultSetIdleTime    

The request parameter resultSetTTL is the time (in seconds) that the client requests that the result set created should be maintained.  The server MAY choose not to fulfill this request, and may respond with a different value, via the response element resultSetIdleTime.

resultSetIdleTime is a good-faith estimate by the server of the idle time, in seconds. That is, the server projects (but does not guarantee) that the result set will remain available and unchanged (both in content and order) until there is a period of inactivity exceeding this idle time. The idle time must be a positive integer, and should not be so small that a client cannot realistically reference the result set again. If the server does not intend that the result set be referenced, it should omit the result set identifier in the response.

The response element resultSetIdleTime may be less-than, equal-to, or greater-than the request parameter resultSetTTL, and may be supplied or omitted regardless of whether resultSetTTL is supplied or omitted.  Thus the two  (from a protocol point of view) are independent. 

5.5    Stylesheet

The request parameter ‘stylesheet’ is a URL for a stylesheet. The client requests that the server simply return this URL in the response, in the href attribute of the xml-stylesheet processing instruction before the response xml. (It is likely that the type will be XSL, but not necessarily so.) If the server cannot fulfill this request it must supply a non-surrogate diagnostic .

The purpose is to allow a thin client to turn the response XML into a natively renderable format, often HTML or XHTML. This allows a web browser, or other application capable of rendering stylesheets, to act as a dedicated client without requiring any further application logic.




This requests the server to include the following as beginning of the response:

<?xml version="1.0"?>

 <?xml-stylesheet type="text/xsl" href="/master.xsl"?>

 <sru:searchRetrieveResponse ...

5.6    records

The response element ‘records’ is a sequence of <record> elements.  See Structure of the <Record> Element. Each contains either a record, or a surrogate diagnostic explaining why that record could not be transferred.  All records are transferred in XML. Records may be expressed as a single string, or as embedded XML. If a record is transferred as embedded XML, it must be well formed and should be validatible against the record schema.

5.7    diagnostics

The response element ‘diagnostics’ includes one or more non-surrogate diagnostics.

Note:  See Diagnostic Model.  Non-surrogate diagnostics are distinguished from surrogate diagnostics. The latter occur in the 'records' element of the response (they take the place of the record for which they are a surrogate). Non-surrogate diagnostics, both fatal and non-fatal, occur in the 'diagnostics' element.

5.8    extraRequestData, extraResponseData, and extraRecordData

The request parameter  extraRequestData’; response element <extraResponseData>, shown in Response Schema for SRU 1.2;  and the <extraRecordData> element listed in  Structure of the Record Element,  are fields in which additional information may be provided. The mechanism is described in Extensions.

5.9     echoedSearchRetrieveRequest

The response element <echoedSearchRetrieveRequest> is  as shown in the example below. Note the two sub-elements <xQuery> and <baseUrl>.

<xQuery> represents an XCQL [reference]  rendering of the query.

Note: This has two benefits.

·         The client can use XSLT or other XML manipulation to modify the query without having a CQL query parser.

·         The server can return extra information specific to the clauses within the query.

<baseURL> allows the client to reconstruct queries by simple concatenation, or retrieve the explain document to fetch additional information such as the title and description to include in the results presented to the user.

Echoed Request Example




        <query>dc.title = dinosaur</query>



              <searchClause xmlns="">












6      Response Schema for SRU 1.2

An example of a searchRetrieve response:





              record 1 …. See Example Record



             record 2 …..






         …. see Echoed Request Example







        first non-surrogate diagnostic … see Non Surrogate Diagnostic Example





        second non-surrogate diagnostic






              see Extension Example



6.1    Structure of the <Record> Element

Each <record> element is structured into the elements shown in the following table.




Table 3: Structure of the <Record> Element








The URI identifier of the XML schema in which the record is encoded. Although the request may use the server's assigned short name, the response must always be the full URI.




'string' or 'xml'.




The actual  record.






An identifier for the record by which it can unambiguously be retrieved in a subsequent operation. For example via the 'rec.identifier' index in CQL.




The position of the record within the result set.




Any additional information to be transferred with the record.


An example record, in the simple Dublin Core schema, packed as XML:

                  <srw_dc:dc xmlns:srw_dc="info:srw/schema/1/dc-v1.1">
                       <dc:title>This is a Sample Record</dc:title>
             <rel:score xmlns:rel="info:srw/extensions/2/rel-1.0"> 0.965 </rel:score>


7      Diagnostics

7.1    Diagnostic List

Diagnostics for use with SRU 1.2 are listed at This diagnostic list has the namespace: info:srw/diagnostic/1. For example, the URI info:srw/diagnostic/1/10 identifies the diagnostic “Query syntax error”. 

 Diagnostics used in SRU 1.2 need not be limited to this list, nor need this list be used exclusively for SRU 1.2.

7.2    Diagnostic Schema

The diagnostic schema for SRU 1.2 has three elements, 'uri', 'details' and 'message'.

The required 'uri' field is a URI, identifying the particular diagnostic. The 'details' part contains information specific to the diagnostic. The 'message' field contains a human readable message to be displayed. Only the uri field is required, the other two are optional.

The identifier for the diagnostic schema is: info:srw/schema/1/diagnostics-v1.1

Table 3: Elements of the Diagnostic Schema








The diagnostic's identifying URI.




Any supplementary information available, often in a format specified by the diagnostic




A human readable message to display to the end user. The language and style of this message is determined by the server, and clients should not rely on this text being appropriate for all situations.

7.3    Diagnostic Examples

7.3.1    Non-Surrogate Example

Non-surrogate, fatal diagnostic:


     <diagnostic xmlns="">



            <message>Too many boolean operators, the maximum is 10.

                               Please try a less complex query.</message>



7.3.2    Surrogate Example

Surrogate, non-fatal diagnostic:



         <recordSchema> info:srw/schema/1/diagnostics-v1.1</recordSchema>


              <diagnostic xmlns="">


                     <message>Record deleted by another user.</message>



     </record> ...


8      Extensions

The name for an extension must begin with 'x-' (lower case x followed by hyphen. SRU 1.2 and future versions will never include an official extension with a name beginning with 'x-', so this will never clash with a mainstream extension name.) It is recommended that the extension name be 'x-' followed by an identifier for the namespace for the extension, again followed by a hyphen, followed by the name of the element within the namespace.


Note that this convention does not guarantee uniqueness since the extension name will not include a full URI. The extension owner should try to make the name as unique as possible. If the namespace is identified by an 'info:srw' URI , then the recommended convention is to name the extension "x-infoNNN-XXX" where NNN is the 'info:srw' authority string, and XXX is the name of the extension. Extension names MUST never be assigned with this form except by the proper authority for the given 'info' namespace.


The response may include extraResponseData  with any well-formed XML, and hence servers can include namespaced XML fragments within it in order to convey information back to the client. The extension MUST supply a namespace and the element names with which to do this, if feedback to the client is necessary.



 <auth:token xmlns:auth="info:srw/extension/2/auth-1.0">




Semantics: If the server does not understand a piece of information in an extension parameter, it may silently ignore it. This is unlike many other request parameters, where if the server does not implement that particular feature it MUST respond with a diagnostic. If the particular request requires some confirmation that it has been carried out rather than ignored, then the extension designer should include a field in the response. The semantics of parameters in the request may not be modified by extensions, however the semantics of parts of the response may be modified by extensions. The response semantics may be changed in this way only if the client specifically requests the change. Clients should in any case be prepared to receive the regular semantics, as servers are at liberty to ignore extensions.

 ExtraResponseData may be sent that is not directly associated with the request. For example it may contain cost information regarding the query or information on the server or database supplying the results. This data must, however, have been requested. As the request may be echoed, the server must be able to transform the elements into their XML form. If it encounters an unrecognized element, the server may either make its best guess as to how to transform the element, or simply not return it at all. It should not, however, add an undefined namespace to the element as this would invalidate the response. If the content of the element is an XML structure, then the extension designer should also specify how to encode this structure in a URL. This may simply be to escape all of the special characters, but the designer could also create a string encoding form with rules as to how to generate the XML in much the same fashion as the relationship between CQL and XCQL.



The following individuals have participated in the creation of this specification and are gratefully acknowledged:


Kerry Blinco, Australian Department of Education, Employment and Workplace Relations

Ray Denenberg, Library of Congress

Larry Dixson, Library of Congress

Matthew Dovey, JISC

Janifer Gatenby, OCLC/PICS

Ralph LeVan, OCLC

Ashley Sanders, University of Manchester

Rob Sanderson, University of Liverpool

A.  SRU/CQL 2.0 Features

Non-normative Annex

A.1 Background

This specification of the SRU 1.2 Binding is a straightforward rendering of and is equivalent to the existing SRU 1.2 specification. It was developed as a proof of concept for the Abstract Protocol Definition (as is the Open Search binding). The CQL Committee Draft is similarly a straightforward rendering of the CQL 1.2 specification.

Now the OASIS SWS Technical Committee turns its attention to substantive changes to SRU and CQL, one of the reasons for the creation of the committee.  This annex describes some of the changes that have been contemplated. The list that follows is neither a complete list, nor have any of the proposals in this list been approved at any level. The purpose of this list of proposals is to generate discussion on these and other proposals.

A.2 Proposed Changes for SRU 2.0 and CQL 2.0

A.2.1 Allow Non-XML Record Representations

Although SRU does not require the database to store  records as XML, it does require it to transfer the data as XML. Many formats do not map easily into XML, for example multimedia, images and even complex text formats. This proposal is to allow non-xml serialized data in the response, signaled by additional values for the recordPacking parameter.   Two possible values are:

A.2.2 Proximity as Boolean Modifier

The proposal is to deprecate the PROX BOOLEAN operator and instead have a BOOLEAN  prox modifier, with the same modifiers: ‘unit’, ‘distance’ and ‘ordered’. The rationale for doing this is twofold.

Proximity would then look like:

A.2.3 Proximity as Relation

Alternatively proximity can be represented as a searchClause:. add a new relation to CQL called ‘window’ allowing full proximity, rather than just adjacency as is currently possible. CQL.’window’ would take the full range of proximity modifiers: ‘distance’, ‘unit’ and ‘ordered’. For example:

This proposal also allows for more than 2 terms to be part of a proximity query (however only as relates to a single index):

A.2.4 Parenthesized Terms

The above window relation does not allow choice. Window is the equivalent of “all” in that regard. For


This is the only way this query can be expressed. And there are other applications for this style of query.

A.2.5 Faceted Searching

Faceted searching is commonly supported by search engines; for example, one might wish to do a search on a database for books about a particular topic and then see how many records there are in different time periods.

The proposed change is to add a new, optional response element for faceted results.   In addition there would be a request parameter to request faceted results.

A.2.6 Result Set Size

The proposal is to add a parameter allowing the client to indicate how much effort the server should take to determine or estimate the number of records in the result set. Similarly, the response might include a parameter indicating how accurate is the result-set-size reported.

The server may be able to determine the exact number of records, or provide a realistic estimate, but it may be an expensive process. The server might prefer not go through that process unless the client requests that it do so.  Or the client might want to explicitly request that the server go through or not go through that process.

 For example, the client might want the first 10 records regardless of how many there are. In that case if the server goes through the process of determining how many records there are, it may go through an expensive process for nothing.

There is also the (special) case where the server cannot determine or estimate the number of records in the result set. In that case it might be useful to have a special value or some way to indicate this condition.

A.2.7 Multiple Query Types

The proposal is to support multiple query types. CQL would be one query type but there could be other query types as well, for example, Parameterized Query and XQuery.

There are a number of possible ways to integrate support for multiple queries into the protocol.

A.2.8 Eliminate the Version and Operation Parameters

The version parameter in SRU is based on the assumption that the same base URL is to be used for multiple versions of the protocol, and SRU prescribes a mechanism to allow different versions to attempt to interoperate. Instead, different base URLs could be used for different versions, base URLs and corresponding versions exposed via explain, and then a client would know the version of a server, so there would never be a mismatch.

Similarly, the operation parameter could be eliminated on the same basis.