SPARQL- A query language for RDF(s)

SPARQL - A QUERY LANGUAGE FOR RDF(S)Fred Freitas - CIn/UFPE - Brazil

QUERY LANGUAGES: SQL(SQL QUERY LANGUAGE) [ORACLE 2006] A language for querying collections of tuples: SELECT SALARY, HIRE_DATE FROM EMPS WHERE EMP_ID = 13954

EMP_ID NAME HIRE_DATE SALARY

13954 Joe 2000-04-14 48000

10335 Mary 1998-11-23 52000

… … … …

04182 Bob 2005-02-10 21750

QUERY LANGUAGES: XQUERY(XML QUERY) [ORACLE 2006]

A language for querying trees of XDM nodes: for $e in document(my_employees.xml) where $emp/emp/@emp-id = 13954 return $emp/emp/salary

e m p-id = 1 39 54

Joe

< n a m e>

2 0 00 -04 -14

< h ire -d a te>

4 80 00

< sa la ry>

< e m p>

...

< e m p>

...

< e m p>

...

< e m p>

< e m p lo ye e s>

Chapter 3 A Semantic Web Primer4

WHY AN RDF QUERY LANGUAGE?DIFFERENT XML REPRESENTATIONS

XML at a lower level of abstraction than RDF There are various ways of syntactically

representing an RDF statement in XML Thus we would require several XQuery queries,

e.g. //uni:lecturer/uni:title if uni:title element //uni:lecturer/@uni:title if uni:title attribute Both XML representations equivalent!

TWO BASIC FAMILIES OF SQL-LIKE LANGAGES FOR RDF(S)

RDQL Implementations: Jena, Sesame, RDFStore, ...

RQL Implementations: RQL, SPARQL, ...

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INTRODUCTION TO RDQL RDF Data Query Language JDBC/ODBC friendly

Simple:

SELECTsome information

FROMsomewhere

WHEREthis match

ANDthese constraints

USINGthese vocabularies

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EXAMPLE

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EXAMPLE

q1 contains a query:

SELECT ?x

WHERE (?x, <http://www.w3.org/2001/vcard-rdf/3.0#FN>, "John Smith")

For executing q1with a model m1.rdf:

java jena.rdfquery --data m1.rdf --query q1

The outcome is:

x

=============================

<http://somewhere/JohnSmith/>

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EXAMPLE

Return all the resources that have property FN and the associated values:

SELECT ?x, ?fname

WHERE (?x, <http://www.w3.org/2001/vcard-rdf/3.0#FN>, ?fname)

The outcome is:

x | fname

================================================

<http://somewhere/JohnSmith/> | "John Smith"

<http://somewhere/SarahJones/> | "Sarah Jones"

<http://somewhere/MattJones/> | "Matt Jones"

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EXAMPLE

Return the first name of Jones:

SELECT ?givenName

WHERE (?y, <http://www.w3.org/2001/vcard-rdf/3.0#Family>, "Jones"),

(?y, <http://www.w3.org/2001/vcard-rdf/3.0#Given>, ?givenName)

The outcome is:

givenName

=========

"Matthew"

"Sarah"

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URI PREFIXES : USING

RDQL has a syntactic convenience that allows prefix strings to be defined in the USING clause :

SELECT ?x WHERE (?x, vCard:FN, "John Smith") USING vCard FOR <http://www.w3.org/2001/vcard-rdf/3.0#>

SELECT ?givenNameWHERE (?y, vCard:Family, "Smith"),

(?y, vCard:Given, ?givenName) USING vCard FOR <http://www.w3.org/2001/vcard-rdf/3.0#>

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FILTERS

RDQL has a syntactic convenience that allows prefix strings to be defined in the USING clause :

SELECT ?resource WHERE (?resource, info:age, ?age) AND ?age >= 24 USING info FOR <http://somewhere/peopleInfo#>

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LIMITATIONS

Does not take into account semantics of RDF(S) For example:

ex:human rdfs:subClassOf ex:animalex:student rdfs:subClassOf ex:humanex:john rdf:type ex:student

Query: “ To which class does the resource John belong?”Expected answer: ex:student, ex:human, ex:animalHowever, the query:

SELECT ?xWHERE (<http://example.org/#john>, rdf:type, ?x)USING rdf FOR <http://www.w3.org/1999/02/22-rdf-syntax-ns#>

Yields only:<http://example.org/#student>

Solution: Inference Engines

SPARQL

SPARQL is a recursive acronym standing for SPARQL Protocol and RDF Query Language

It provides facilities to [Staab 2006]:extract information in the form of URIs,

blank nodes, plain and typed literals. extract RDF subgraphs. construct new RDF graphs based on

information in the queried graphs

GRAPH PATTERNS

Basic Graph Pattern – set of Triple Patterns

Group Pattern - a set of graph patterns must all match

Value Constraints - restrict RDF terms in a solution

Optional Graph Patterns .- additional patterns may extend the solution

Alternative Graph Pattern – two or more possible patterns are tried

Patterns on Named Graphs - patterns are matched against named graphs

BASIC GRAPH PATTERN

Set of Triple Patterns Triple Pattern – similar to an RDF Triple (subject,

predicate, object), but any component can be a query variable; literal subjects are allowed

Matching a triple pattern to a graph: bindings between variables and RDF Terms

Matching of Basic Graph Patterns A Pattern Solution of Graph Pattern GP on graph G is

any substitution S such that S(GP) is a subgraph of G.

x v

rdf:type rdf:Property

rdf:type rdf:type rdf:Property

SELECT ?x ?v WHERE { ?x ?x ?v }

?book dc:title ?title

BASIC GRAPH PATTERN - MULTIPLE MATCHES

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

SELECT ?name ?mbox

WHERE

{ ?x foaf:name ?name .

?x foaf:mbox ?mbox }

@prefix foaf: <http://xmlns.com/foaf/0.1/> .

_:a foaf:name "Johnny Lee Outlaw" .

_:a foaf:mbox <mailto:[email protected]> .

_:b foaf:name "Peter Goodguy" .

_:b foaf:mbox <mailto:[email protected]> .

name mbox

"Johnny Lee Outlaw"

<mailto:[email protected]>

"Peter Goodguy" <mailto:[email protected]>

Group Graph Pattern (set of graph patterns) also!

Data

Query

Query Result

BASIC GRAPH PATTERN - BLANK NODES

PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?x ?name

WHERE { ?x foaf:name ?name }


_:a foaf:name "Alice" .

_:b foaf:name "Bob" .

x name

_:c “Alice“

_:d “Bob”

Data

Query

Query Result

GRAPH PATTERNS







GROUP PATTERN


SELECT ?name ?mbox

WHERE

{ ?x foaf:name ?name .

?x foaf:mbox ?mbox }


SELECT ?name ?mbox

WHERE

{ {?x foaf:name ?name;

foaf:mbox ?mbox }

}

GRAPH PATTERNS







VALUE CONSTRAINTS

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 .

?x dc:title ?title . }

@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> .

@prefix ns: <http://example.org/ns#> .

:book1 dc:title "SPARQL Tutorial" .

:book1 ns:price 42 .

:book2 dc:title "The Semantic Web" .


title price

"The Semantic Web" 23

Data

Query

Query Result

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REGULAR EXPRESSIONS CAN BE USED

PREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX ldap: <http://ldap.hp.com/people#>PREFIX foaf:

SELECT ?name ?name2{ ?doc dc:title ?title . FILTER regex(?title, “SPARQL”) . ?doc dc:creator ?reseacher . ?researcher ldap:email ?email . ?researcher ldap:name ?name}

• “Find the name and email addresses of authors of a paper about SPARQL”

GRAPH PATTERNS







OPTIONAL GRAPH PATTERNS

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

PREFIX ns: <http://example.org/ns#>

SELECT ?title ?price

WHERE { ?x dc:title ?title .

OPTIONAL { ?x ns:price ?price .

FILTER ?price < 30 }}

@prefix dc: <http://purl.org/dc/elements/1.1/> .

@prefix : <http://example.org/book/> .

@prefix ns: <http://example.org/ns#> .

:book1 dc:title "SPARQL Tutorial" .


:book2 dc:title "The Semantic Web" .


title price

“SPARQL Tutorial“

"The Semantic Web" 23

Data

Query

Query Result

MULTIPLE OPTIONAL BLOCKS


SELECT ?name ?mbox ?hpage

WHERE { ?x foaf:name ?name .

OPTIONAL { ?x foaf:mbox ?mbox }. OPTIONAL { ?x foaf:homepage ?hpage } }


@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .


_:a foaf:homepage <http://work.example.org/alice/> .



Data

Query

Query Result

name Mbox hpage

“Alice“ <http://work.example.org/alice/>

“Bob“ <mailto:[email protected]>

GRAPH PATTERNS

Basic Graph Patterns – set of Triple Patterns

Group Patterns - a set of graph patterns must all match



Alternative Graph Patterns – two or more possible patterns are tried


ALTERNATIVE GRAPH PATTERNS

PREFIX dc10: <http://purl.org/dc/elements/1.0/>

PREFIX dc11: <http://purl.org/dc/elements/1.1/>

SELECT ?x ?y

WHERE { { ?book dc10:title ?x } UNION { ?book dc11:title ?y } }

@prefix dc10: <http://purl.org/dc/elements/1.0/> .

@prefix dc11: <http://purl.org/dc/elements/1.1/> .

_:a dc10:title "SPARQL Query Language Tutorial" .

_:b dc11:title "SPARQL Protocol Tutorial" .

_:c dc10:title "SPARQL" .

_:c dc11:title "SPARQL (updated)" .

Data

Query

Query Result

x y

"SPARQL (updated)"

"SPARQL Protocol Tutorial"

"SPARQL"

"SPARQL Query Language Tutorial"

GRAPH PATTERNS







RDF DATASET RDF data stores may hold multiple RDF graphs:

record information about each graph queries that involve information from more than one

graph RDF Dataset in SPARQL terminology the background graph, which does not have a name,

and zero or more named graphs, identified by URI reference

the relationship between named and background graphs: (i) to have information in the background graph that

includes provenance information about the named graphs (the application is not directly trusting the information in the named graphs )

(ii) to include the information in the named graphs in the background graph as well.

RDF DATASET- THE RELATIONSHIP BETWEEN NAMED AND BACKGROUND GRAPHS (I)

# Background graph

@prefix dc: <http://purl.org/dc/elements/1.1/> .

<http://example.org/bob> dc:publisher "Bob" .

<http://example.org/alice> dc:publisher "Alice" .

# Graph: http://example.org/bob


_:a foaf:name "Bob" .


# Graph: http://example.org/alice




RDF DATASET- THE RELATIONSHIP BETWEEN NAMED AND BACKGROUND GRAPHS (II)

# Background graph

@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:x foaf:name "Bob" .

_:x foaf:mbox <mailto:[email protected]> .

_:y foaf:name "Alice" .

_:y foaf:mbox <mailto:[email protected]> .

# Graph: http://example.org/bob


_:a foaf:name "Bob" .


# Graph: http://example.org/alice




QUERYING THE DATASET# Graph: http://example.org/foaf/aliceFoaf


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

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .



_:a foaf:knows _:b .

_:b rdfs:seeAlso <http://example.org/foaf/bobFoaf> .

<http://example.org/foaf/bobFoaf> rdf:type foaf:PersonalProfileDocument .



_:b foaf:age 32 . # Graph: http://example.org/foaf/bobFoaf


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

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

_:1 foaf:mbox <mailto:[email protected]> .

_:1 rdfs:seeAlso <http://example.org/foaf/bobFoaf> .

_:1 foaf:age 35 .

<http://example.org/foaf/bobFoaf> rdf:type foaf:PersonalProfileDocument .

QUERYING THE DATASET - ACCESSING GRAPH LABELS


SELECT ?src ?bobAge

WHERE { GRAPH ?src

{ ?x foaf:mbox <mailto:[email protected]> .

?x foaf:age ?bobAge }

}

src bobAge

<http://example.org/foaf/aliceFoaf> 32

<http://example.org/foaf/bobFoaf> 35

QUERYING THE DATASET - RESTRICTING BY GRAPH LABEL


PREFIX data: <http://example.org/foaf/>

SELECT ?age

WHERE

{

GRAPH data:bobFoaf {

?x foaf:mbox <mailto:[email protected]> .

?x foaf:age ?age }

}

age

35

QUERYING THE DATASET - RESTRICTING VIA QUERY PATTERN

PREFIX data: <http://example.org/foaf/>


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

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

SELECT ?mbox ?age ?ppd

WHERE

{ GRAPH data:aliceFoaf

{ ?alice foaf:mbox <mailto:[email protected]> ;

foaf:knows ?whom .

?whom foaf:mbox ?mbox ;

rdfs:seeAlso ?ppd .

?ppd a foaf:PersonalProfileDocument . } .

GRAPH ?ppd { ?w foaf:mbox ?mbox ;

foaf:age ?age } }

mbox age ppd

<mailto:[email protected]> 35 <http://example.org/foaf/bobFoaf>

CONSTRUCTING AN OUTPUT GRAPH

Data:@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:givenname "Alice" . _:a foaf:family_name "Hacker" . _:b foaf:firstname "Bob" . _:b foaf:surname "Hacker" .

Query:PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> CONSTRUCT { ?x vcard:N _:v . _:v vcard:givenName ?gname . _:v vcard:familyName ?fname } WHERE { { ?x foaf:firstname ?gname } UNION { ?x foaf:givenname ?gname } . { ?x foaf:surname ?fname } UNION { ?x foaf:family_name ?fname } . }

Result:@prefix vcard:

<http://www.w3.org/2001/vcard-rdf/3.0#> . _:v1 vcard:N _:x . _:x vcard:givenName "Alice" . _:x vcard:familyName "Hacker" . _:v2 vcard:N _:z . _:z vcard:givenName "Bob" . _:z vcard:familyName "Hacker" .

ASK – A BOOLEAN QUERY


@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .


_:a foaf:homepage <http://work.example.org/alice/> .




ASK { ?x foaf:name "Alice" }

TRUE.

CONCLUSIONS

Several query languages for RDF/RDF(S) Some (not exclusive) SPARQL advantages

Inferencing Implicit and explicit joins Once the schemas are defined elsewhere in

RDF/RDF(S) too, they can also be queried upon! Many facilities: regex, datatypes, functions,... Queries built similarly to SQL... But also over graphs (in opposition to flat

relational DBs).

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ANY QUESTİONS?

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SPARQL- A query language for RDF(s)