introduzione ad xml - politecnico di milanohome.deib.polimi.it/colombet/ke/materiale/ke exe...

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SPAR-QL

Mario Arrigoni Neri

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Introduction

SPARQL = SPARQL Protocol and RDF Query Language

SPARQL - query language to manipulate information in RDF graphs. It provides support to:

– 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

matching graph patterns

variables – global scope; indicated by ‘?‘ or ‘$‘

query terms – based on Turtle syntax

terms delimited by "<>" are relative URI references

data description format - Turtle

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N-Triple → Turtle → N3

N-Triple:

- is an extremely constrained language which uses hardly any syntactic sugar

- optimized for reading by scripts, and comparing using text tools

- just allows one triple on each line.

Turtle:

- some syntactic sugar for more compact and human readable files

N3:

- chains

- rules

- RDF superset (eg: literals as subjects, quantification, formulae)

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Turtle

Turtle adds the following syntax to N-Triples:

ASCII -> UTF-8 @prefix, @base Qnames , ; [] A () xsd:integer xsd:double xsd:decimal xsd:boolean

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Turtle examples : @prefix , ;

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

<http://example.org/path> a doc:Document .

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

:x a :Person;

:knows :y.


:x :knows :y, :z.

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Turtle examples : []


:x a :Person;

:knows [ a :VIP.].


:x a :Person;

:knows :mark,

[ a :VIP; :lives-in :Italy;

:has-job :actor, :singer.

].

:mark a :Student; :lives-in :UK.

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SPARQL - Basic graph patterns

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

?book dc:title ?title

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Basic graph patterns - 2

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

SELECT ?x ?v

WHERE { ?x ?x ?v }

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Basic graph patterns - 2

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

SELECT ?x ?v

WHERE { ?x ?x ?v }

rdf:type rdf:type rdf:Property

x v

rdf:type rdf:Property

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Multiple Matches

@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]> .

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

SELECT ?name ?mbox

WHERE { ?x foaf:name ?name .

?x foaf:mbox ?mbox }

name mbox

"Johnny Lee Outlaw"

<mailto:[email protected]>

"Peter Goodguy"

<mailto:[email protected]>

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Blank nodes


_:a foaf:name "Alice" .

_:b foaf:name "Bob" .

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

WHERE { ?x foaf:name ?name }

x name

_:c “Alice“

_:d “Bob”

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Group patterns


SELECT ?name ?mbox

WHERE

{ ?x foaf:name ?name .

?x foaf:mbox ?mbox } PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?mbox

WHERE

{ {?x foaf:name ?name;

foaf:mbox ?mbox } }

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Value constraints

@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" .


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 . }

title price

"The Semantic Web" 23

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Optional graph patterns

@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" .



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

SELECT ?title ?price

WHERE { ?x dc:title ?title .

OPTIONAL { ?x ns:price ?price .

FILTER ?price < 30 }

}

title price

“SPARQL Tutorial“

"The Semantic Web" 23

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Multiple optional blocks


@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/> .


_:b foaf:mbox <mailto:[email protected]> . PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?mbox ?hpage

WHERE { ?x foaf:name ?name .

OPTIONAL { ?x foaf:mbox ?mbox }.

OPTIONAL { ?x foaf:homepage ?hpage } }

name Mbox hpage

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

“Bob“ <mailto:[email protected]>

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Alternative graph patterns

@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)" .

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 } }

x y

"SPARQL (updated)"

"SPARQL Protocol Tutorial"

"SPARQL"

"SPARQL Query Language Tutorial"

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Evaluation order

Optional-1: an optional pattern that has a common variable with a(more) basic graph pattern(s) must be executed after the basic graph pattern(s)

Optional-2: there can't be two optional patterns with a common variable, if that variable does not occur in a basic graph pattern

Constraint: constraints are evaluated after values are assigned to variables

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RDF Dataset

RDF data stores may hold multiple RDF graphs:– store 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) information in the background graph that includes

provenance information about the named graphs (the application does not directly trust the information in the named graphs )

– (ii) include the information in the named graphs in the background graph.

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RDF Dataset - 2

# 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/alice




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


_:a foaf:name "Bob" .


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RDF Dataset - 3

# Background graph


_:x foaf:name "Bob" .

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

_:y foaf:name "Alice" .

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

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




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


_:a foaf:name "Bob" .


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Querying dataset

# Graph: http://example.org/foaf/aliceFoaf




_:a foaf:name "Alice";

foaf:mbox <mailto:[email protected]>;

foaf:knows _:b .

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

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

_:b foaf:name "Bob";

foaf:mbox <mailto:[email protected]>;

foaf:age 32 .

# Graph: http://example.org/foaf/bobFoaf




_: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 .

mailto:[email protected]

mailto:[email protected]

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Querying dataset


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

SELECT ?age

WHERE

{

GRAPH data:bobFoaf {

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

foaf:age ?age }

}

Resticting by graph label

age

35

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Querying dataset


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

Accessing graph labels

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Querying dataset

PREFIX .....

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 } }

Resticting via query pattern

mbox age ppd

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

PREFIX .....

SELECT ?mbox ?age ?ppd

WHERE

{ GRAPH data:aliceFoaf

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

[foaf:mbox ?mbox ; rdfs:seeAlso ?ppd.].

?ppd a foaf:PersonalProfileDocument . } .

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

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Query forms

– SELECT • returns all, or a subset of the variables bound in a

query pattern match• formats : XML or RDF/XML

– CONSTRUCT • returns an RDF graph constructed by substituting

variables in a set of triple templates – DESCRIBE

• returns an RDF graph that describes the resources

found. – ASK

• returns whether a query pattern matches or not.

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Construct




@prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>.

<http://example.org/person#Alice> vcard:FN "Alice" .

CONSTRUCT { <http://example.org/person#Alice> vcard:FN ?name } WHERE { ?x foaf:name ?name }

#extracting a whole graph from the target RDF dataset

CONSTRUCT { ?s ?p ?o }

WHERE { GRAPH <http://example.org/myGraph> { ?s ?p ?o } . }

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Describe

PREFIX ent: <http://myorg.example/employees#>

DESCRIBE ?x

WHERE { ?x ent:employeeId "1234" }


@prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0> .

@prefix myOrg: <http://myorg.example/employees#> .

_:a myOrg:employeeId "1234" ;

foaf:mbox_sha1sum "ABCD1234" ;

vcard:N [ vcard:Family "Smith" ;

vcard:Given "John" ] .

foaf:mbox_sha1sum rdf:type owl:InverseFunctionalProperty .

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Ask


@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/> .


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


ASK { ?x foaf:name "Alice" } .

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Order, limit, offlset


SELECT ?name

WHERE { ?x foaf:name ?name }

ORDER BY ?name

LIMIT 5

OFFSET 10

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Group by, having, aggregation

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

SELECT (AVG(?size) AS ?asize)

WHERE {

?x :size ?size

}

GROUP BY ?x

HAVING(AVG(?size) > 10)

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SparQL 1.1 - Federated queries


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

:people15 foaf:name "Alice" .

:people16 foaf:name "Bob" .

:people17 foaf:name "Charles";

foaf:interest <http://www.w3.org/2001/sw/rdb2rdf/> .


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

:people15 foaf:knows :people18 .

:people18 foaf:name "Mike" .

:people17 foaf:knows :people19 .

:people19 foaf:name "Daisy" ..

http://people.example.org/sparql

http://people2.example.org/sparql

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SparQL 1.1 - Federated queries


SELECT ?name ?interest ?known

WHERE

{

SERVICE <http://people.example.org/sparql> {

?person foaf:name ?name .

OPTIONAL {

?person foaf:interest ?interest .

SERVICE <http://people2.example.org/sparql> {

?person foaf:knows ?known . } }

}

}"Alice""Bob""Charles" <http://www.w3.org/2001/sw/rdb2rdf/> <http://example.org/people19>

http://www.w3.org/2001/sw/rdb2rdf/

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SparQL 1.1 – update


INSERT DATA

{

<http://example/book1> dc:title "A new book" ;

dc:creator "A.N.Other" .

}


DELETE DATA

{

<http://example/book2> dc:title "David Copperfield" ;

dc:creator "Edmund Wells" .

}

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SparQL 1.1 – update


WITH <http://example/addresses>

DELETE { ?person foaf:givenName 'Bill' }

INSERT { ?person foaf:givenName 'William' }

WHERE

{ ?person foaf:givenName 'Bill'. }

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