An Introduction to Linked Data: SPARQL Query Language

An
Introduction
to
Linked Data

Part 4 of 5 David Hyland-Wood
SPARQL Query Language University of Mary Washington

Monday, May 16, 2011

SPARQL:
A query
language for RDF

SPARQL
• Query Language for RDF
http://www.w3.org/TR/rdf-sparql-query

• SPARQL Protocol and RDF Query
Language
• Graph pattern based language
written the same as Turtle

• Several queries — Ask; Select;
Describe; Construct
• Read Only
still vulnerable to injection, though not as bad as SQL


Queries
• ASK — True or False
Simple, Fast

• SELECT — Tabular data
easy to work with

• DESCRIBE — RDF
whatever the store has

• CONSTRUCT — RDF
Whatever you want


a /discipline/ rdfs:label
space:Discipline Space Physics
spacephysics

foaf:name
Sputnik 1
space:discipline

dc:description
The Sputnik 1 spacecraft was ...

space:agency
U.S.S.R
a /spacecraft/
space:Spacecraft
1957-001B space:mass
86.3

foaf:depiction
/images/sputnik.jpg
space:spacecraft

space:launched
1957-10-04
a
space:Launch /launch/1957-001
space:launchvehicle
Modiﬁed SS-6 (Sapwood)

space:launchsite

rdfs:label
Tyuratam (Baikonur Cosmodrome)
a
space:Launchsite /launchsite/tyurata
space:country
U.S.S.R


Triple Patterns


Triple Patterns

<http://example.com/spacecraft/1957-001B>
foaf:name "Sputnik 1" .


Triple Patterns


?something foaf:name "Sputnik 1" .


Triple Patterns



?something foaf:name ?name .


Triple Patterns



?something foaf:name ?name .

ASK WHERE {
}


spacephysics

foaf:name
Sputnik 1
space:discipline
dc:description

space:agency
U.S.S.R
a /spacecraft/
space:Spacecraft
86.3

foaf:depiction
/images/sputnik.jpg
space:spacecraft

space:launched
1957-10-04
a
space:launchvehicle

space:launchsite

rdfs:label
a Tyuratam (Baikonur Cosmodrome)
space:country
U.S.S.R


Triple Patterns
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

ASK WHERE {
?something rdfs:label ?label .
}


Triple Patterns

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

ASK WHERE {
?something rdfs:label ?label ;
rdf:type space:Discipline .
}


Triple Patterns

PREFIX space: <http://purl.org/net/schemas/space/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

ASK WHERE {
?spacecraft foaf:name “Sputnik 1” .
?launch space:spacecraft ?spacecraft .
?launch space:launched ?launchdate .
}


Example SELECT


SELECT ?subject ?label WHERE {

?subject rdfs:label ?label ;
a space:Discipline .

}


Example SELECT
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
<head>
<variable name="subject"/>
<variable name="label"/>
</head>
<results>
<result>
<binding name="subject">
<uri>http://nasa.dataincubator.org/discipline/astronomy</
uri>
</binding>
<binding name="label">
<literal>Astronomy</literal>
</binding>
</result>
<result>
<uri>http://nasa.dataincubator.org/discipline/
communications</uri>
</binding>
<binding name="label">
<literal>Communications</literal>
</binding>
</result>


Example SELECT


SELECT * WHERE {

?subject rdfs:label ?label ;
a space:Discipline .

}


Example SELECT DISTINCT


SELECT DISTINCT ?date WHERE {

?launch space:launched ?date .

}


Example OPTIONAL


SELECT ?name ?image WHERE {

?spacecraft foaf:name ?name .

OPTIONAL {
?spacecraft foaf:depiction ?image .
}
}


Example OPTIONAL
<?xml version="1.0"?>
<head>
<variable name="name"/>
<variable name="image"/>
</head>
<results>
<result>
<binding name="name">
<literal>Soyuz 2</literal>
</binding>
</result>
<result>
<binding name="name">
<literal>Apollo 10</literal>
</binding>
<binding name="image">
<uri>http://nssdc.gsfc.nasa.gov/image/spacecraft/
apollo_10_cm.jpg</uri>
</binding>
</result>


Example UNION


SELECT ?subject ?displayLabel WHERE {
{
?subject foaf:name ?displayLabel .
}
UNION
{
?subject rdfs:label ?displayLabel .
}
}


Example UNION
<?xml version="1.0"?>
<head>
<variable name="subject"/>
<variable name="displayLabel"/>
</head>
<results>
<result>
<uri>http://nasa.dataincubator.org/spacecraft/ATLAS2</uri>
</binding>
<binding name="displayLabel">
<literal>Atlas 2</literal>
</binding>
</result>
<result>
<uri>http://nasa.dataincubator.org/spacecraft/ATLAS3</uri>
</binding>
<binding name="displayLabel">
<literal>Atlas 3</literal>
</binding>
</result>


Example ORDER BY


SELECT ?name ?launchdate WHERE {
}


Example ORDER BY


}
ORDER BY DESC(?launchdate)


Example ORDER BY


}
LIMIT 10


Example ORDER BY


}
LIMIT 10
OFFSET 10


Example FILTER

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

SELECT ?name WHERE {
?launch space:launched ?date ;
space:spacecraft ?spacecraft .

FILTER (
?date >= "1969-01-01"^^xsd:date &&
?date <= "1969-12-31"^^xsd:date
)
}


Example FILTER


SELECT ?spacecraft ?name WHERE {
?spacecraft foaf:name ?name ;
space:mass ?mass .

FILTER( xsd:double(?mass) < 90.0 )
}


Example FILTER


SELECT ?name WHERE {


FILTER( regex(?name, “ollo”, “i” ) )
}


Built-in Filters
• Logical (!, &&, ||)
• Math (+, -, *, /)
• Comparison (=, !=, >, <, ...)
• Tests
isURI, isBlank, isLiteral, bound, sameTerm, langMatches, regex

• Accessors
str, lang, datatype


Example NOT


SELECT ?s WHERE {

?s a space:Spacecraft .

OPTIONAL {
?s foaf:depiction ?image .
}

FILTER ( !bound(?image) )
}


Example DESCRIBE

DESCRIBE <http://example.com/launch/1969-059>


Example DESCRIBE
<rdf:RDF
xmlns:space="http://purl.org/net/schemas/space/"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" >

<rdf:Description
rdf:about="http://nasa.dataincubator.org/launch/1969-059">
<space:spacecraft
rdf:resource="http://nasa.dataincubator.org/spacecraft/1969-059C"/>
<space:spacecraft
rdf:resource="http://nasa.dataincubator.org/spacecraft/1969-059B"/>
<space:spacecraft
rdf:resource="http://nasa.dataincubator.org/spacecraft/1969-059A"/>
<space:launchvehicle>Saturn 5</space:launchvehicle>
<space:launchsite
rdf:resource="http://nasa.dataincubator.org/launchsite/capecana..."/>
<space:launched
rdf:datatype="http://www.w3.org/2001/XMLSchema#date">
1969-07-16
</space:launched>
<rdf:type
rdf:resource="http://purl.org/net/schemas/space/Launch"/>
</rdf:Description>
</rdf:RDF>


Example DESCRIBE


DESCRIBE ?spacecraft WHERE {

?launch space:launched "1969-07-16"^^xsd:date .
?spacecraft space:launch ?launch .

}


Example DESCRIBE
<rdf:RDF
xmlns:space="http://purl.org/net/schemas/space/"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:foaf="http://xmlns.com/foaf/0.1/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema#" >
<rdf:Description rdf:about="http://nasa.dataincubator.org/spacecraft/1969-059B">
<foaf:homepage rdf:resource="http://nssdc.gsfc.nasa.gov/database/MasterCatalog?
sc=1969-059B"/>
<dc:description>The...</dc:description>
<space:mission rdf:resource="http://nasa.dataincubator.org/mission/apollo-11"/>
<space:agency>United States</space:agency>
<rdf:type rdf:resource="http://purl.org/net/schemas/space/Spacecraft"/>
<space:launch rdf:resource="http://nasa.dataincubator.org/launch/1969-059"/>
<space:discipline rdf:resource="http://nasa.dataincubator.org/discipline/
planetaryscience"/>
<space:alternateName>04040</space:alternateName>
<space:alternateName>Apollo 11 Saturn V third stage</space:alternateName>
<foaf:name>Apollo 11 SIVB</foaf:name>
<space:internationalDesignator>1969-059B</space:internationalDesignator>
<space:mass>13300.0</space:mass>
</rdf:Description>

...


Example DESCRIBE


DESCRIBE ?spacecraft ?launch WHERE {

?launch space:launched "1969-07-16"^^xsd:date .
?spacecraft space:launch ?launch .

}


Example CONSTRUCT


CONSTRUCT {
space:agency ?agency ;
space:launched ?launchdate .
}
WHERE {
space:agency ?agency .
}


spacephysics

foaf:name
space:discipline Sputnik 1

dc:description

space:agency
U.S.S.R
a /spacecraft/
space:Spacecraft
86.3

foaf:depiction
/images/sputnik.jpg
space:spacecraft

space:launched
1957-10-04
a
space:launchvehicle

space:launchsite

rdfs:label
Tyuratam (Baikonur Cosmodrome)
a
space:country
U.S.S.R


spacephysics

foaf:name
Sputnik 1
space:discipline
dc:description

space:agency
U.S.S.R
a /spacecraft/
space:Spacecraft
86.3

foaf:depiction
/images/sputnik.jpg
space:spacecraft
space:launched

space:launched
1957-10-04
a
space:launchvehicle

space:launchsite

rdfs:label
space:country
U.S.S.R


Common Problems
• Typos
wrong case for property or class name

• wrong preﬁx URI
missing # or / or the URI for the web page

• Missing OPTIONAL
you won't even notice...

• Comparing Literals
Literals are compared on all of value, type and language


Tip 1: Find all the Properties

SELECT DISTINCT ?p WHERE {

?s ?p ?o .

}


spacephysics

foaf:name
Sputnik 1
space:discipline

dc:description

space:agency
U.S.S.R
a /spacecraft/
space:Spacecraft
86.3

foaf:depiction
/images/sputnik.jpg
space:spacecraft

space:launched
1957-10-04
a
space:launchvehicle

space:launchsite

rdfs:label
space:country
U.S.S.R


a rdfs:label
/discipline/
spacephysics

foaf:name
Sputnik 1
space:discipline
dc:description

space:agency
U.S.S.R
a /spacecraft/
space:Spacecraft
86.3

foaf:depiction
/images/sputnik.jpg
space:spacecraft

space:launched
a 1957-10-04
space:launchvehicle

space:launchsite

rdfs:label
space:country
U.S.S.R


Tip 2: Find all the Classes

SELECT DISTINCT ?type WHERE {

?s a ?type .

}


Thanks to

• Rob Styles, Talis Group Ltd for his CC-BY
licensed “Two Day Introduction to the Web of
Data” slides and spacecraft example data.


This work is Copyright © 2010 David Hyland-Wood
Based partially on CC-BY licensed content Copyright © 2010 Talis Systems Limited by Rob Styles.
It is licensed under the Creative Commons Attribution 3.0 Unported License.
Full details at: http://creativecommons.org/licenses/by/3.0/

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• For any reuse or distribution, you must make clear to others the license terms of this work.
• Any of the above conditions can be waived if you get permission from the copyright holder.
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