Alexandra Cristea 1. pronounced "sparkle“ recursive acronym for: ◦ SPARQL Protocol and...

SPARQL Intro:A query language for RDF

Alexandra Cristea

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pronounced "sparkle“ recursive acronym for:

◦ SPARQL Protocol and RDF Query Language a semantic query language a query language for RDF(S) W3C Recommendation 15th January 2008

◦ provides a standard format for writing queries that target RDF data ◦ and a set of standard rules for processing queries and returning the results

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

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What is SPARQL

New version: 21st of March 2013: http://www.w3.org/TR/sparql11-overview/ Query language at: http://www.w3.org/TR/sparql11-query/ Implemented in various programming

languages

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SPARQL now

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RDF Statements

SubjectPredicate

author http://www.w3schools.com/RDF

Object

Jan Egil Refsnes

SPARQL searches for all sub-graphs that match the graph described by the triples in the query.

?subject ?predicate ?object

SELECT ?studentWHERE { ?student b:studies bmod:CS414 }

~ SQL – why?Which are the namespace prefixes?

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A sample of SPARQL

In RDF:<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-

syntax-ns#" xmlns:cd="http://www.recshop.fake/cd#">

In SPARQL:PREFIX b: <http://...>

PREFIX bmod: <http://www2.warwick.ac.uk/fac/sci/dcs/teaching/material/>

The PREFIX keyword is SPARQL’s version of an xmlns:namespace declaration and works in basically the same way.

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Prefixes & namespaces

Prefix IRI

rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#

rdfs: http://www.w3.org/2000/01/rdf-schema#

xsd: http://www.w3.org/2001/XMLSchema#

fn: http://www.w3.org/2005/xpath-functions#

sfn: http://www.w3.org/ns/sparql#

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Frequently used namespaces

Prefixes are not optional in SPARQL!

Capitals of Europe: http://liris.cnrs.fr/~pchampin/spark/gmapv3.html

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Dbpedia + Google maps mashup

http://dbpedia.org/sparql http://dbpedia.org/isparql/ http://dbpedia.org/snorql/ http://querybuilder.dbpedia.org/index.php

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DbPedia Query points

http://dbpedia.org/resource/The_Lord_of_the_Rings http://dbpedia.org/resource/Berlin http://dbpedia.org/resource/Category:Cities_in_Englan

d http://dbpedia.org/resource/The_Beatles - Fluidops http://dbpedia.org/resource/Paul_McCartney http://dbpedia.org/resource/Category:English_musician

s http://dbpedia.org/resource/Semantic_Web http://dbpedia.org/resource/Tetris http://dbpedia.org/resource/SPARQL

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Sample Resources

OpenLink Query point◦ http://demo.openlinksw.com/sparql

Semanticweb.org data:◦ http://data.semanticweb.org/snorql/

Diseases:◦ http://wifo5-03.informatik.uni-mannheim.de/diseasome/snorql/

Country statistics:◦ http://wifo5-03.informatik.uni-mannheim.de/factbook/snorql/

Nobelprize info:◦ http://data.nobelprize.org/snorql/

W3C’s list of endpoints:◦ http://www.w3.org/wiki/SparqlEndpoints

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Other SPARQL query points

http://www.sparql.org/query.html http://sparql.org/sparql.html http://demo.openlinksw.com/sparql

◦ make sure to allow at ‘Sponging’ to ‘Retrieve remote RDF data for all missing source graphs’

http://librdf.org/query

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Online SPARQL queries

Different syntax from XMLVariables: begin with ? or $ triples patterns enclosed within braces {}Result: variables after SELECT (~SQL)

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SPARQL basics

PREFIX foo: PREFIX bar: SELECT … FROM … WHERE {…} GROUP BY … HAVING … ORDER BY … LIMIT … OFFSET … VALUES …

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Anatomy of a Query

~ SQL

SELECT queries CONSTRUCT queries ASK queries DESCRIBE queries

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4 Types of SPARQL Queries

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?x ?y ?zFROM <http://www.w3.org/People/Berners-Lee/card>WHERE { ?x ?y ?z }

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PREFIX SELECT FROM WHERE

PREFIX b: <http://www2.warwick.ac.uk/rdf/>PREFIX bmod:

<http://www2.warwick.ac.uk/fac/sci/dcs/teaching/material/>

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

SELECT ?name

WHERE { ?student b:studies bmod:CS328 .

?student foaf:name ?name }

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Combining conditions

FOAF (Friend Of A Friend) experimental project using RDF, defining a

standardised vocabulary. Goal: make personal homepages machine-

readable & understandable, create an internet-wide connected database of people.

Defined at:http://xmlns.com/foaf/0.1/

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FOAF

Idea: most personal homepages contain similar info.◦E.g, person’s name, living place, work place, details

on work of the moment, links to friends.◦define RDF predicates to represent them. ◦So: Pages: understood/ manipulated by computers.

So a db can be queried for: ◦“what projects are my friends working on?”, ◦“do any of my friends know the director of

BigCorp?” etc..

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FOAF

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-

ns#" xmlns:foaf="http://xmlns.com/foaf/0.1#"> <foaf:Person> <foaf:name>Alexandra I. Cristea</foaf:name> <foaf:mbox rdf:resource="mailto:a.i.cristea@warwick.ac.uk"/> </foaf:Person> </rdf:RDF>

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A sample FOAF RDF document

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:foaf="http://xmlns.com/foaf/0.1/"> <foaf:Person> <foaf:name>Peter Brusilovsky</foaf:name> <foaf:firstName>Peter</foaf:firstName> <foaf:surname>Brusilovsky</foaf:surname> <foaf:mbox_sha1sum>1fa1a097b3fae4594fa0ec18e2e3da11ac7e0349</foaf:mbox_sha1sum> <foaf:knows> <foaf:Person> <foaf:name>Alexandra I. Cristea</foaf:name> <foaf:mbox_sha1sum>dba246a0d9ec4a6238198f9a035a7a608ff227f8</foaf:mbox_sha1sum> <rdfs:seeAlso rdf:resource="http://www.dcs.warwick.ac.uk/~acristea/"/> </foaf:Person> </foaf:knows> </foaf:Person> </rdf:RDF>

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FOAF: another example

PREFIX b: <http://www2.warwick.ac.uk/rdf/>PREFIX bmod: <

http://www2.warwick.ac.uk/fac/sci/dcs/teaching/material/>PREFIX foaf:http://xmlns.com/foaf/0.1/

SELECT ?module ?nameWHERE { ?student b:studies ?module . ?student foaf:name ?name }

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Extracting multiple results

PREFIX b: <http://www2.warwick.ac.uk/rdf/>PREFIX bmod: <

http://www2.warwick.ac.uk/fac/sci/dcs/teaching/material/ >

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

SELECT ?module ?name

WHERE { ?student b:studies ?module ; foaf:name ?name }

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Using the same subject

SELECT ?module ?nameWHERE { ?student b:studies ?module . ?student b:studies bmod:CS328 ; foaf:name ?name }

is identical to:

SELECT ?module ?name

WHERE { ?student b:studies ?module , bmod:CS328 ;

foaf:name ?name }

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Abbreviating multiple objects

SELECT ?student ?emailWHERE { ?student b:studies mod:CS328 . ?student foaf:mbox ?email }

PB: if a student does not have an e-mail address registered, with a foaf:mbox predicate, then the query will not match !!

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Optional graph components

SELECT ?student ?emailWHERE { ?student b:studies mod:CS328 .OPTIONAL { ?student foaf:mbox ?email } }

OPTIONAL: match it if it can, but otherwise not reject the overall pattern.

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Optional graph components

SPARQL basics SPARQL endpoints: dbpedia, foaf, others SPARQL type of queries:

◦ SELECT; CONSTRUCT; ASK; DESCRIBE SQL-like constructs:

◦ SELECT; FROM; WHERE; GROUP BY; HAVING; ORDER BY; LIMIT; OFFSET; VALUES

Some specific constructs:◦ PREFIX not optional; FROM not always used; OPTIONAL◦ We are going to look at more specific constructs

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We have studied:

Try out at: http://www.sparql.org/query.html

PREFIX books: <http://example.org/book/>PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT $book WHERE {$book title $title } >> this gives an empty answer/ error.

Versus:PREFIX books: <http://example.org/book/>PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT $book WHERE {$book dc:title $title } 28

Prefixes are not optional

try out at : http://www.sparql.org/query.htmlWith or without optionalPREFIX books: <http://example.org/book/>PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT ?book ?author ?title ?dateWHERE { ?book dc:creator ?author . ?book dc:title ?title . ?book dc:date ?date }

PREFIX books: <http://example.org/book/>PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT ?book ?author ?title ?dateWHERE { ?book dc:creator ?author . ?book dc:title ?title . OPTIONAL { ?book

dc:date ?date } } 29

OPTIONAL query example

Try analysing RDF documents e.g.: http://athena.ics.forth.gr:9090/RDF/VRP/Examples/tap.rdf (on http://sparql.org/sparql.html or Protégé, or specific endpoints) Using SPARQL to find Concepts endpoints Dbpedia SNORQL query explorer (http://dbpedia.org/snorql/),

the BBC Backstage SPARQL Editor (http://bbc.openlinksw.com/sparql) or GeoSparql (http://geosparql.org/) to analyse content.

Listing DISTINCT RDF Types The following query lists the distinct rdf:types used in a dataset PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>SELECT DISTINCT ?typeWHERE { ?s rdf:type ?type } Listing OWL ClassesPREFIX owl: <http://www.w3.org/2002/07/owl#>SELECT ?classWHERE { ?class a owl:Class } 30

Analysing documents

SELECT ?module ?name ?phoneWHERE { ?student b:studies ?module . ?student foaf:name ?name .OPTIONAL { ?student b:contactpermission true .?student b:phone ?phone} }

SELECT ?module ?name ?ageWHERE { ?student b:studies ?module . ?student foaf:name ?name .OPTIONAL { ?student b:age ?age . FILTER (?age > 25) } }

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More optional graph components …and filters:

SELECT ?student ?email ?homeWHERE { ?student b:studies mod:CS328 .OPTIONAL { ?student foaf:mbox ?email . ?student foaf:homepage ?home } }

SELECT ?student ?email ?homeWHERE { ?student b:studies mod:CS328 .OPTIONAL { ?student foaf:mbox ?email } .OPTIONAL { ?student foaf:homepage ?home } }

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Further optional examples …

SELECT ?studentWHERE { ?student foaf:mbox ?email . { ?student b:studies mod:CS328 } UNION { ?student b:studies mod:CS909 } }

When patterns are combined using the UNION keyword, the resulting combined pattern will match if any of the subpatterns is matched.

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Combining matches

Consider A and B as graph patterns. { A } UNION { B }

◦ Either / or graph patterns◦ Disjunction; include both the results of solving A and the

results of solving B { A } MINUS { B }

◦ “subtracted” graph patterns (SPARQL 1.1)◦ Negation; Solve A; Solve B; Include only those results from A

that are not compatible with any of the results from B.

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Combining SPARQL Graph Patterns

All the previous queries: single RDF graphs. Often: multiple RDF graphs. RDF graphs: identified by IRI.

◦ Note: IRI that represents the graph does not have to be the actual IRI of the graph file

◦ although the program processing the query will need to somehow relate the IRI to an actual RDF graph stored somewhere.

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Multiple graphs and the dataset

SELECT ?student ?email ?homeFROM <http://www2.warwick.ac.uk/rdf/student>WHERE { ?student b:studies mod:CS414 . OPTIONAL { ?student foaf:mbox ?email . ?student foaf:homepage ?home } }

By using several FROM declarations, you can combine several graphs in the dataset:

SELECT ?student ?email ?homeFROM <http://www2.warwick.ac.uk/rdf/student>FROM <http://www2.warwick.ac.uk/rdf/foaf>WHERE { ?student b:studies mod:CS414 . OPTIONAL { ?student foaf:mbox ?email . ?student foaf:homepage ?home } }

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Stating the dataset

one (optional) default graph + any number of named graphs. FROM specifies default graph.

◦Many FROM keywords, the graphs are merged into the default graph.

Additionally: named graphs, w FROM NAMED.◦However, to match patterns you must use GRAPH

keyword to state which graph !

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Multiple graphs

SELECT ?student ?email ?homeFROM NAMED <http://www2.warwick.ac.uk/rdf/student>FROM NAMED<http://www2.warwick.ac.uk/rdf/foaf>

WHERE { GRAPH <http://www2.warwick.ac.uk/rdf/student> { ?student b:studies mod:CS909 } . GRAPH <http://www2.warwick.ac.uk/rdf/foaf> { OPTIONAL { ?student foaf:mbox ?email . ?student foaf:homepage ?home } } }

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Examples of named graphs

PREFIX brdf: <http://www2.warwick.ac.uk/rdf/>SELECT ?student ?email ?homeFROM NAMED <http://www2.warwick.ac.uk/rdf/student>FROM NAMED <http://www2.warwick.ac.uk/rdf/foaf>

WHERE { GRAPH brdf:student { ?student b:studies mod:CS909 } . GRAPH brdf:foaf{ OPTIONAL { ?student foaf:mbox ?email . ?student foaf:homepage ?home } } }

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Abbreviation using prefixes

PREFIX brdf: <http://www2.warwick.ac.uk/rdf/>SELECT ?student ?email ?homeFROM <http://www2.warwickac.uk/rdf/student>FROM NAMED <http://www2.warwickac.uk/rdf/foaf>

WHERE { ?student b:studies mod:CS909 . GRAPH brdf:foaf{ OPTIONAL { ?studentfoaf:mbox?email . ?studentfoaf:homepage ?

home } } } 40

Using named and default graph together

the GRAPH can also be a variable.◦to query which graph in the dataset holds a

particular relationship, ◦or which graph to search based on data in

another graph.

not mandatory to declare all graphs◦even if specified, the dataset can be

overridden on a per-query basis.

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Graph as a query

PREFIX brdf: <http://www2.warwick.ac.uk/rdf/>SELECT ?student ?graphWHERE { ?student b:studies mod:CS909 . GRAPH ?graph { ?student foaf:mbox ?email } }

output var graph holds graph URL (matching student to e-mail address).

Presumption: query processor has knowledge of a finite set of graphs + their locations

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Which graph is it in?

PREFIX brdf: <http://www2.warwickac.uk/rdf/>SELECT ?student ?emailWHERE { ?student b:studies mod:CS909 . ?student rdfs:seeAlso ?graph . GRAPH ?graph { ?student foaf:mbox ?email } } Note: if student doesn’t have a rdfs:seeAlso property

which points to a graph holding their e-mail address, they will not appear in the result at all.

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Re-using the graph reference

Specific SPARQL constructs: ◦ Revisited OPTIONAL, PREFIX, FROM - single◦ New ones: FILTER, UNION, MINUS, FROM –multiple,

FROM NAMED, GRAPH, GRAPH with prefix, GRAPH as (query-able + reusable) variable

More online/ offline queries:◦ Endpoints◦ Sparql.com◦ Protégé

Next: other SQL-like constructs; non-SQL-like behaviour: ASK, DESCRIBE, CONSTRUCT

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We have learned:

SELECT ?name ?moduleWHERE { ?student b:studies ?module . ?student foaf:name ?name }ORDER BY ?name

SELECT ?name ?ageWHERE { ?student b:age ?age . ?student foaf:name ?name }ORDER BY DESC (?age) ASC (?name)

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Sorting results of a query

SELECT ?name ?moduleWHERE { ?student b:studies ?module .?student foaf:name ?name }LIMIT 20

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Limiting the number of results

SELECT ?name ?moduleWHERE { ?student b:studies ?module . ?student foaf:name ?name }ORDER BY ?nameOFFSET 10LIMIT 20

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Extracting subsets of the results

SELECT ?studentWHERE { ?student b:studies ?module }

versus:

SELECT DISTINCT ?studentWHERE { ?student b:studies ?module }

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Obtaining unique results

Is any student studying any module?ASK { ?student b:studies ?module }

Is any student studying CS909?ASK { ?student b:studies bmod:CS909 }

Is student 029389 studying CS909?ASK { bstu:029389 b:studies bmod:CS909 }

Is anyone whom 029389 knows, studying CS909?ASK {bstu:029389 foaf:knows ?x .

?x b:studies bmod: CS909 } Is any student aged over 30 studying CS909? ASK { ?student b:studies bmod:CS909 . ?student b:age ?age . FILTER { ?age > 30 } }

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Obtaining a Boolean result

CONSTRUCT { ?student b:studyFriend ?friend }WHERE { ?student b:studies ?module . ?student foaf:knows ?friend . ?friend b:studies ?module } }

If there is more than one search result, the triples from each result are combined.

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Constructing an RDF result

DESCRIBE ?country

Result is in RDF triples, in any RDF serialization

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DESCRIBE queries

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[1] Dean Allemang & Jim Hendler. 2008 Semantic Web for the working ontologist. Morgan Kaufmann publishers. ISBN 978-0-12-373556-0

[2] Eric Prud'hommeaux ; & Andy Seaborne . 2008 SPARQL Query Language for RDF , [Online] http://www.w3.org/TR/rdf-sparql-query/

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References

Download Jena from http://jena.sourceforge.net/ Protégé 3.4 and above

http://protege.stanford.edu/ Fuseki:

http://jena.apache.org/documentation/serving_data/index.html

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Tools to process

SPARQL language is used for querying RDF. SPARQL is not based on XML, but on SQL-

like syntax. Building blocks of SPARQL queries are graph

patterns that include variables. The result of the query will be the values the vars must take to match the RDF graph.

A SPARQL query can return results in several different ways, as determined by the query.

SPARQL queries can also be used for OWL querying.

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Summary

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Questions?