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AbstractRDF 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 .
1. IntroductionThe 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].
There are two other results formats which follow a similar design but do not use XML: SPARQL 1.1 Query Results JSON Format [SRJ] and SPARQL 1.1 Query Results CSV and TSV Formats [SRC].
2. DefinitionDefinition: 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 ElementThe 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.
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.
The results element contains the complete sequence of query results.
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:
<binding><uri>U</uri></binding>
<binding><literal>S</literal></binding>
<binding><literal xml:lang="L">S</literal></binding>
<binding><literal datatype="D">S</literal></binding>
<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 result-to-html.xq giving output-xquery.html or with XSLT sheet result-to-html.xsl giving output-xslt.html
3.2. Boolean Results ExamplesAn 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 result-to-html.xq giving output-xquery2.html or with XSLT sheet result-to-html.xsl giving output-xslt2.html
4. XML SchemasThere are normative XML schemas provided in the following formats:
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/2007/SPARQL/result.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".
Internet Media Type Registration FormSPARQL 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.
[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.
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