W3C

SPARQL Query Results XML Format

W3C Candidate Recommendation 25 September 2007

This version:
http://www.w3.org/TR/2007/CR-rdf-sparql-XMLres-20070925/
Latest version:
http://www.w3.org/TR/rdf-sparql-XMLres/
Previous version:
http://www.w3.org/TR/2007/WD-rdf-sparql-XMLres-20070614/
Editors:
Dave Beckett, Institute for Learning and Research Technology (ILRT), University of Bristol
Jeen Broekstra, Information Systems Group, Eindhoven University of Technology

Copyright ©2007 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

Abstract

RDF is a flexible, extensible way to represent information about World Wide Web resources. It is used to represent, among other things, personal information, social networks, metadata about digital artifacts like music and images, as well as provide a means of integration over disparate sources of information. A standardized query language for RDF data with multiple implementations offers developers and end users a way to write and to consume the results of queries across this wide range of information.

This document describes an XML format for the variable binding and boolean results formats provided by the SPARQL query language for RDF, developed by the W3C RDF Data Access Working Group (DAWG), part of the Semantic Web Activity as described in the activity statement .

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This 25 Sep 2007 draft, along with the other working drafts for SPARQL, is a Candidate Recommendation; it been widely reviewed and satisfies the requirements documented in RDF Data Access Use Cases and Requirements ; W3C publishes a Candidate Recommendation to gather implementation experience.

The first release of this document was 21 Dec 2004 and the RDF Data Access Working Group has made its best effort to address comments received since then, releasing several drafts and resolving a list of issues meanwhile. The design has stabilized and the Working Group intends to advance this specification to Proposed Recommendation once the exit criteria below are met:

This specification will remain a Candidate Recommendation until at least 9 October 2007. An implementation report will be produced.

Comments on this document should be sent to public-rdf-dawg-comments@w3.org, a mailing list with a public archive.

Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1. Introduction

The SPARQL Query Language for RDF [SPARQL-QUERY] defines several Query Result Forms (SPARQL Query section 10). This document defines a SPARQL Results Document that encodes the variable binding query results from SELECT queries (SPARQL Query section 10.2) and boolean query results from ASK queries (SPARQL Query section 10.5) in XML [XML].

2. Definition

Definition: SPARQL Results Document

A SPARQL Results Document is an XML document that is valid with respect to either the RELAX NG XML Schema or the W3C XML Schema in Section 4.

2.1. Document Element

The SPARQL Results Document begins with sparql document element in the http://www.w3.org/2005/sparql-results# namespace, written as follows:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
 ...
</sparql>

Inside the sparql element are two sub-elements, head and a results element (either results or boolean) which must appear in that order.

2.2. Header

The head element is the first child element of the sparql element.

For a variable binding query result, head must contain a sequence of elements describing the set of Query Variable names in the Solution Sequence (here called query results).

The order of the variable names in the sequence is the order of the variable names given to the argument of the SELECT statement in the SPARQL query. If SELECT * is used, the order of the names is undefined.

Inside the head element, the ordered sequence of variable names chosen are used to create empty child elements variable with the variable name as the value of an attribute name giving a document like this:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">

  <head>
    <variable name="x"/>
    <variable name="hpage"/>
    <variable name="name"/>
    <variable name="mbox"/>
    <variable name="blurb"/>
  </head>
...
</sparql>

For a boolean query result, no elements are required inside head and variable must not be present.

For any query result, head may also contain link child elements with an href attribute containing a relative URI that provides a link to some additional metadata about the query results. The relative URI is resolved against the in-scope base URI which is usually the query results format document URI. link elements must appear after any variable elements that are present.

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">

  <head>
    ...
    <link href="metadata.rdf"/>
  </head>
...
</sparql>

2.3. Results

The second child-element of sparql must appear after head and is either results or boolean. It is written even if the query results are empty.

2.3.1. Variable Binding Results

The results element contains the complete sequence of query results.

NOTE: in previous versions of this document the results element had two required attributes, distinct and ordered. Both attributes have been removed (see change log entry for 2007-05-03).

For each Query Solution in the query results, a result child-element of results is added giving a document like:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
  ...  head ...

  <results>
    <result>...
    </result>
    <result>...
    </result>
    ...
  </results>

</sparql>

Each result element corresponds to one Query Solution in a result and contains child elements (in no particular order) for each Query Variable that appears in the solution. It is used to record how the query variables bind to RDF Terms.

Each binding inside a solution is written as an element binding as a child of result with the query variable name as the value of the name attribute. So for a result binding two variables x and hpage it would look like:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
  <head>
    <variable name="x"/>
    <variable name="hpage"/>
  </head>

  <results>
    <result>
      <binding name="x"> ... </binding>
      <binding name="hpage"> ... </binding>
    </result>

    <result>
      <binding name="x"> ... </binding>
      <binding name="hpage"> ... </binding>
    </result>
    ...
  </results>

</sparql>

The value of a query variable binding, which is an RDF Term, is included as the content of the binding as follows:

RDF URI Reference U
<binding><uri>U</uri></binding>
RDF Literal S
<binding><literal>S</literal></binding>
RDF Literal S with language L
<binding><literal xml:lang="L">S</literal></binding>
RDF Typed Literal S with datatype URI D
<binding><literal datatype="D">S</literal></binding>
Blank Node label I
<binding><bnode>I</bnode></binding>

If, for a particular solution, a variable is unbound, no binding element for that variable is included in the result element.

Note: The blank node label I is scoped to the result set XML document and need not have any association to the blank node label for that RDF Term in the query graph.

An example of a query solution encoded in this format is as follows:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">

  <head>
    <variable name="x"/>
    <variable name="hpage"/>
    <variable name="name"/>
    <variable name="age"/>
    <variable name="mbox"/>
    <variable name="friend"/>
  </head>

  <results>

    <result> 
      <binding name="x">
	<bnode>r2</bnode>
      </binding>
      <binding name="hpage">
	<uri>http://work.example.org/bob/</uri>
      </binding>
      <binding name="name">
	<literal xml:lang="en">Bob</literal>
      </binding>
      <binding name="age">
	<literal datatype="http://www.w3.org/2001/XMLSchema#integer">30</literal>
      </binding>
      <binding name="mbox">
	<uri>mailto:bob@work.example.org</uri>
      </binding>
    </result>

    ...
  </results>

</sparql>

2.3.2. Boolean Results

A boolean result is written as the element content of a boolean child-element of the sparql element directly after a head, containing either true or false as follows:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
  ...  head ...

  <boolean>true</boolean>

</sparql>

3. Examples

3.1. Variable Binding Results Examples

An example SELECT SPARQL Query in example.rq operating on query graph Turtle/N3 data in data.n3 providing ordered variable binding query results written in XML in output.srx.

This XML can be transformed into XHTML using the sample XML Query script result2-to-html.xq giving output-xquery.html or with XSLT sheet result2-to-html.xsl giving output-xslt.html

3.2. Boolean Results Examples

An example ASK SPARQL Query in example2.rq operating on query graph Turtle/N3 data in data.n3 provides a boolean query result written in XML in output2.srx.

This XML can be transformed into XHTML using the sample XML Query script result2-to-html.xq giving output-xquery2.html or with XSLT sheet result2-to-html.xsl giving output-xslt2.html

4. XML Schemas

There are normative XML schemas provided in the following formats:

  1. RELAX NG[RELAXNG] Compact[RELAXNG-COMPACT] in result2.rnc
  2. RELAX NG XML in result2.rng
  3. W3C XML Schema[XMLSCHEMA-1] in result2.xsd
    Note: this schema is machine-generated from the RELAX NG XML schema.

If W3C XML Schema is used, an xsi:schemaLocation attribute can be used pointing to the schema as follows:

<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://www.w3.org/TR/2007/CR-rdf-sparql-XMLres-20070925/result2.xsd">

  ...

</sparql>

5. Internet Media Type, File Extension and Macintosh File Type

The Internet Media Type / MIME Type for the SPARQL Query Results XML Format is "application/sparql-results+xml".

It is recommended that result files have the extension ".srx" (all lowercase) on all platforms.

It is recommended that result files stored on Macintosh HFS file systems be given a file type of "TEXT".

This information that follows is intended to be submitted to the IESG for review, approval, and registration with IANA.

Internet Media Type Registration Form

To: ietf-types@iana.org
Subject: Registration of media type application/sparql-results+xml

Type name:
application
Subtype name:
sparql-results+xml
Required parameters:
None
Optional parameters:
"charset": This parameter has identical semantics to the charset parameter of the "application/xml" media type as specified in [RFC3023], section 3.2.
Encoding considerations:
Identical to those of "application/xml" as specified in [RFC3023], section 3.2.
Security considerations:

SPARQL query results uses URIs. See Section 7 of [RFC3986].

SPARQL query results uses IRIs. See Section 8 of [RFC3987].

As this media type uses the "+xml" convention, it shares the same security considerations as described in [RFC3023], section 10.

Interoperability considerations:
There are no known interoperability issues.
Published specification:
This specification.
Applications which use this media type:
No known applications currently use this media type.
Additional information:
Magic number(s):
As specified for "application/xml" in [RFC3023], section 3.2.
File extension(s):
".srx"
Fragment identifiers:
Identical to that of "application/xml" as described in RFC 3023 [RFC3023], section 5.
Base URI:
As specified in [RFC3023], section 6.
Macintosh file type code(s):
"TEXT"
Person & email address to contact for further information:
Dave Beckett, Eric Prud'hommeaux <public-rdf-dawg-comments@w3.org>
Intended usage:
COMMON
Restrictions on usage:
None
Author/Change controller:
The SPARQL specification is a work product of the World Wide Web Consortium's RDF Data Access Working Group. The W3C has change control over these specifications.

References

[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.

[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005.

6. References

[XML]
Extensible Markup Language (XML) 1.0, Third Edition, T. Bray, J. Paoli, C.M. Sperberg-McQueen, E. Maler, F. Yergeau, Editors, W3C Recommendation, 4 February 2004. This document is http://www.w3.org/TR/2004/REC-xml-20040204 . The latest version is available at http://www.w3.org/TR/REC-xml .
[SPARQL-QUERY]
SPARQL Query Language for RDF, E. Prud'hommeaux, A. Seaborne, Editors, W3C Working Draft (work in progress), 21 July 2005. This document is http://www.w3.org/TR/2005/WD-rdf-sparql-query-20050721/ . The latest version is available at http://www.w3.org/TR/rdf-sparql-query/ .
[RELAXNG]
RELAX NG Specification, James Clark and MURATA Makoto, Editors, OASIS Committee Specification, 3 December 2001. This document is http://www.oasis-open.org/committees/relax-ng/spec-20011203.html . The latest version is available at http://www.oasis-open.org/committees/relax-ng/spec.html .
[RELAXNG-COMPACT]
RELAX NG Compact Syntax, James Clark, Editor. OASIS Committee Specification, 21 November 2002. This document is http://www.oasis-open.org/committees/relax-ng/compact-20021121.html .
[XMLSCHEMA-1]
XML Schema Part 1: Structures Second Edition, D. Beech, N. Mendelsohn, M. Maloney, H. S. Thompson, Editors, W3C Recommendation, 28 October 2004. This document is http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/ . The latest version is available at http://www.w3.org/TR/xmlschema-1/ .

A. Changes (Informative)

2007-05-03. The attributes 'ordered' and 'distinct' of the 'results' element have been removed per WG decision at 2007-05-01 telcon.

2005-12-21. Unbound variables are no longer explicitly encoded, instead binding element for such variables is left out. Restriction on order of binding elements inside a solution is dropped. Cf. WG decision at 2005-12-20 telcon.

2005-08-02. Fixed typo, reverted to editor's draft format.

2005-08-01. Published as SPARQL Query Results XML Format, W3C Working Draft 1 August 2005.

For earlier changes see the changes in the 1 August 2005 working draft.