05/01/2016 sparql sparql protocol and rdf query language s. garlatti

22/04/23

SPARQL

SPARQL Protocol and RDF Query Language

S. Garlatti

Computer Science Department Semantic Web in Actionpage 2

Outline

SPARQL


SPARQL: SPARQL Protocol and RDF Query Language

SPARQL

• pronounced "sparkle" [1]) is an RDF query language; its name is a recursive acronym that stands for SPARQL Protocol and RDF Query Language. It is standardized by the RDF Data Access Working Group (DAWG) of the World Wide Web Consortium, and is considered a component of the semantic web.

• Initially released as a Candidate Recommendation in April 2006, but returned to Working Draft status in October 2006, due to two open issues. [2] In June 2007, SPARQL advanced to Candidate Recommendation once again. [3] On 12th November 2007 the status of SPARQL changed into Proposed Recommendation. [4] On 15th January 2008, SPARQL became an official W3C Recommendation. [5]

Computer Science Department


SPARQL =

• A Query Language

• A Result Form

• An Access Protocol

Linked Data & Social Webpage 4



The Query Language: query forms

• « Select » clause returns all or subset of the variables bound in a query pattern match

• « Construct » returns an RDF graph constructed by substituting variables in a set of triple templates

• « Ask » returns a boolean indicating whether a query pattern matches

• « Describe » returns an RDF graph that describe the resources found




« Select » equivalent to « SQL Select » returns a regular table

Select …From … Identify data sources to query

Where { … } The triple/graph pattern to be matched against the triple/graphs of RDF A conjunction of triples

PREFIX to declare the schema used in the query




PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name

FROM <http://example.org/foaf/aliceFoaf>

WHERE { ?x foaf:name ?name } Result:


name

« Alice »



PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX : <http://dbpedia.org/resource/> PREFIX dbpedia2: <http://dbpedia.org/property/> PREFIX dbpedia: <http://dbpedia.org/>

SELECT distinct ?name ?birth ?person

FROM <http://dbpedia.org/>

WHERE

{ ?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin>.

?person dbpedia2:birth ?birth .

?person foaf:name ?name .

}



SPARQL results: namebirthperson« ":Dru_Berrymore/birth/birth_date_and_age :Dru_Berrymore "Dru

Berrymore"@de:Dru_Berrymore/birth/birth_date_and_age :Dru_Berrymore "Walter Benjamin"@de:Berlin :Walter_Benjamin "Walter Benjamin"@de:Germany :Walter_Benjamin

Name Birth Person

« Dru Berrymore »



SELECT distinct ?name ?person FROM <http://dbpedia.org/> WHERE { ?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin> . ?person foaf:name ?name .}

SELECT distinct ?name ?birth ?death ?person FROM <http://dbpedia.org/> WHERE { ?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin> . ?person dbpedia2:birth ?birth . ?person foaf:name ?name . ?person dbpedia2:death ?death.}



A constraint, expressed by the keyword “FILTER”, is a restriction on solutions over the whole group in which the filter appears

PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#>

SELECT ?title ?price

WHERE { ?x ns:price ?price . FILTER (?price < 30.5) ?x dc:title ?title . }




“regex” matches only plain literals with no language tag

{ ?x foaf:name ?name . ?x foaf:mbox ?mbox . FILTER regex(?name, "Smith") }

PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { ?x dc:title ?title FILTER regex(?title, "web", "i" ) }




Optional parts of the graph pattern may be specified syntactically with the “OPTIONAL” keyword applied to a graph pattern

SELECT distinct ?name ?birth ?death ?person FROM <http://dbpedia.org/> WHERE { ?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin> . ?person dbpedia2:birth ?birth . ?person foaf:name ?name . OPTIONAL {?person dbpedia2:death ?death} }




Matching alternative

• Pattern alternatives are syntactically specified with the UNION keyword

SELECT distinct ?name ?birth ?death ?person WHERE { {?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin> }UNION {?person dbpedia2:death ?death} ?person foaf:name ?name . ?person dbpedia2:birth ?birth . }




Sequence & Modify

• « Order By » to sort,

• « LIMIT » result number,

• « OFFSET » rank of first result

SELECT distinct ?name ?person WHERE {?person dbpedia2:birthPlace <http://dbpedia.org/resource/Berlin>.?person foaf:name ?name.} ORDER BY ?name LIMIT 20 OFFSET 20




« Construct »

• The CONSTRUCT query form returns a single RDF graph specified by a graph template.

- The result is an RDF graph formed by taking each query solution in the solution sequence, substituting for the variables in the graph template, and combining the triples into a single RDF graph by set union.

• Useful for aggregating data from multiple sources and merging it into a local store (from Ingenta)




PREFIX foaf: <http://xmlns.com/foaf/0.1/>FROM <http://molene.enstb.org/mlearning09/wp-content/plugins/wp-rdfa/foaf.php

CONSTRUCT {?friend a foaf:Person; foaf:name ?name; foaf:homepage ?home.} WHERE {?person foaf:mbox <mailto:[email protected]>; foaf:knows ?friend.?friend foaf:name ?name; foaf:homepage ?home.}




ASK• Returns a true/false value: test whether or not a query pattern

has a solution.

• No information is returned about the possible query solutions, just whether or not a solution exists

• Is there data that looks like this? Do you have any information about that? (from Ingenta)

PREFIX foaf: <http://xmlns.com/foaf/0.1/> ASK WHERE {?person a foaf:Person; foaf:mbox <mailto:ab@telecom-bretagne>. }

Semantic Web in Actionpage 18



DESCRIBE• The DESCRIBE form returns a single result RDF

graph containing RDF data about resources.

• CONSTRUCT but with less control

- Tell me about this or things that look like this … but you decide what’s relevant (from Ingenta)

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

DESCRIBE ?friend

WHERE {

?person foaf:mbox “mailto:ab@telecom-bretagne”; foaf:knows ?friend.}




Applied uses (from Ingenta)

• DESCRIBE for Prototyping

- DESCRIBE <http://example.org/someResource>

- Quickly assembling Uis, Web APIs

• SELECT for Indexing

- Building an ordering over some data ORDER BY, LIMIT




Applied uses (from Ingenta)

• CONSTRUCT for transformation and also simple inferencing

- CONSTRUCT could be the XSLT of RDF

- Currently limited by lack of expressions in CONSTRUCT triple templates

• ASK for validation

• ASK – DESCRIBE – CONSTRUCT Pattern:

- Probe endpoint, Grab default view of data, Refine data extraction and/or apply transformation




SPARQL Protocol (from F. Gandon, INRIA)

• Sending queries and their results accross the web

Example with HTTP binding

• GET /sparql/?query=<encoded query> HTTP/1.1 Host: www.inria.fr User-agent: my-sparql-client/0.1




Example with SOAP binding (from F. Gandon)

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

xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope/"xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<soapenv:Body><query-request xmlns="http://www.w3.org/2005/09/sparql-protocol-types/#">

<query> SELECT ?x ?p ?y WHERE {?x ?p ?y} </query>

</query-request> </soapenv:Body> </soapenv:Envelope>




Access to Data on the web• http://dbpedia.org/snorql/

• http://dbpedia.org/sparql

• http://demo.openlinksw.com/rdfbrowser2/

• http://dataviewer.zitgist.com/

• Etc.

Twinkle : a sparql query tool

• http://www.ldodds.com/projects/twinkle




Resources

• http://en.wikipedia.org/wiki/SPARQL

• http://www.w3.org/TR/rdf-sparql-query/

• http://jena.sourceforge.net/ARQ/Tutorial/

• http://esw.w3.org/topic/SparqlImplementations

• http://arc.semsol.org/home

• http://virtuoso.openlinksw.com/wiki/main/Main/

05/01/2016 sparql sparql protocol and rdf query language s. garlatti

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