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OWL & SPARQL 2009. 12 Sang-goo Lee School of Computer Science & Engineering Center for E-Business Technology Seoul National University, Seoul, Korea Center for E-Business Technology Seoul National University Seoul, Korea Copyright © 2008~2009 SNU Center for E-Business Technology. All rights reserved. - 웹 정보 시스템 -

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Page 1: OWL & SPARQL - SNUids.snu.ac.kr/w/images/f/f0/wec_2009_owl_sparql.pdf · Center for E-Business Technology OWL & SPARQL -22. Copyright 2009 by CEBT SPARQL SPARQL is a query language

OWL & SPARQL

2009. 12

Sang-goo Lee

School of Computer Science & Engineering

Center for E-Business Technology

Seoul National University, Seoul, Korea

Center for E-Business TechnologySeoul National University

Seoul, Korea

Copyright © 2008~2009 SNU Center for E-Business Technology. All rights reserved.

- 웹 정보 시스템 -

Page 2: OWL & SPARQL - SNUids.snu.ac.kr/w/images/f/f0/wec_2009_owl_sparql.pdf · Center for E-Business Technology OWL & SPARQL -22. Copyright 2009 by CEBT SPARQL SPARQL is a query language

OWL & Description Logics

Page 3: OWL & SPARQL - SNUids.snu.ac.kr/w/images/f/f0/wec_2009_owl_sparql.pdf · Center for E-Business Technology OWL & SPARQL -22. Copyright 2009 by CEBT SPARQL SPARQL is a query language

Copyright 2009 by CEBT

OWL

� Web Ontology Language (WOL? -> OWL)

� is built on top of RDF

� was designed to be interpreted by computers (not people)

� is a W3C Recommendation (standard)

� A richer ontology language

� relations between classes: e.g., disjointness

� cardinality: e.g., “exactly one”

� richer typing of properties

� characteristics of properties (e.g., symmetry)

� Three sublanguages

� OWL Lite - simplest

� OWL DL (includes OWL Lite) - constructs with restriction

� OWL Full (includes OWL DL) - full expressive power

OWL & SPARQL - 3Center for E-Business Technology

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Copyright 2009 by CEBT

OWL

� Basic Structure (OWL Lite)

� (In)Equality: equivalentClass, equivalentProperty , sameAs , differentFrom , AllDifferent , distinctMembers ,

� Property Characteristics: ObjectProperty , DatatypeProperty , inverseOf , TransitiveProperty , SymmetricProperty , FunctionalProperty , InverseFunctionalProperty

� Property Restrictions: Restriction , onProperty , allValuesFrom , someValuesFrom ,

� Restricted Cardinality: minCardinality (only 0 or 1) , maxCardinality (only 0 or 1) , cardinality (only 0 or 1)

� Header Information: Ontology, imports

� Class Intersection: intersectionOf

� Versioning: versionInfo, priorVersion, backwardCompatibleWith, incompatibleWith, DeprecatedClass, DeprecatedProperty

� Annotation Properties: rdfs:label, rdfs:comment, rdfs:seeAlso, rdfs:isDefinedBy, AnnotationProperty, OntologyProperty

� Extended Structure (OWL DL & Full)

� Class Axioms: oneOf, dataRange, disjointWith, equivalentClass, rdfs:subClassOf

� Boolean Combinations of Class Expressions: unionOf, complementOf, intersectionOf

� Arbitrary Cardinality: minCardinality, maxCardinality, cardinality

� Filler Information: hasValue

OWL & SPARQL - 4Center for E-Business Technology

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Copyright 2009 by CEBT

OWL Examples

<owl:Class rdf:about="#associateProfessor">

<owl:disjointWith rdf:resource="#professor"/>

<owl:disjointWith rdf:resource="#assistantProfessor"/>

</owl:Class>

<owl:Class rdf:ID="faculty">

<owl:equivalentClass rdf:resource="#academicStaffMember"/>

</owl:Class>

<owl:ObjectProperty rdf:ID="isTaughtBy">

<owl:domain rdf:resource="#course"/>

<owl:range rdf:resource= "#academicStaffMember"/>

<rdfs:subPropertyOf rdf:resource="#involves"/>

</owl:ObjectProperty>

OWL & SPARQL - 5Center for E-Business Technology

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OWL Examples (cont.)

<owl:ObjectProperty rdf:ID="teaches">

<rdfs:range rdf:resource="#course"/>

<rdfs:domain rdf:resource= "#academicStaffMember"/>

<owl:inverseOf rdf:resource="#isTaughtBy"/>

</owl:ObjectProperty>

<owl:Class rdf:about="#firstYearCourse">

<rdfs:subClassOf>

<owl:Restriction>

<owl:onProperty rdf:resource="#isTaughtBy"/>

<owl:allValuesFrom rdf:resource="#Professor"/>

</owl:Restriction>

</rdfs:subClassOf>

</owl:Class>

OWL & SPARQL - 6Center for E-Business Technology

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Description Logics?

� A family of logic based Knowledge Representation formalisms

� Descendants of semantic networks and KL-ONE

� Describe domain in terms of concepts (classes), roles (relationships)

and individuals

� Distinguished by:

� Formal semantics (typically model theoretic)

– Decidable fragments of FOL

� Provision of inference services

– Sound and complete decision procedures for key problems

OWL & SPARQL - 7Center for E-Business Technology

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DL Basics

� Concepts (unary predicates/formulae with one free variable)

� E.g., Person, Father, Mother

� Roles (binary predicates/formulae with two free variables)

� E.g., hasChild, hasHudband

� Individual names (constants)

� E.g., Alice, Bob, Cindy

� Subsumption (relations between concepts)

� E.g. Female ⊆ Person

� Operators (for forming concepts and roles)

� And(Π) , Or(U), Not (¬)

� Universal qualifier (∀), Existent qualifier(∃)

� Number restriction : ≤, ≥, = � Inverse role (-), transitive role (+), Role hierarchy

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Example

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Role example

� (Inverse Role) hasParent = hasChild-

� hasParent(Bob,Alice) -> hasChild(Alice, Bob)

� (Transitive Role) ancestor+

� ancestor(Bob,David), ancestor(David, Mack) ->

ancestor(Bob,Mack)

� (Role Hierarchy) hasMother ⊆ hasParent

� hasMother(Bob,Alice) -> hasParent(Bob, Alice)

� HappyFather ⊆ Father Π ≥1 hasChild.Woman Π ≥1 hasChild.Man

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OWL as DL: Axioms

[Ian Horrocks]

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OWL as DL: Class Constructors

[Ian Horrocks]

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Knowledge Base

Tbox (schema)

Abox (data)

HappyFather ⊆ Person Π ≥1 hasChild.Woman Π ≥1 hasChild.Man

Happy-Father(Bob)

Inference System

Interface

[Ian Horrocks]

DL Knowledge Base

� Tbox (terminology, taxonomy): a set of axioms describing structure of domain (i.e., a conceptual schema)

� ABox (membership assertions): a set of axioms describing a concrete situation (data), e.g.: John:HappyFather; <John,Mary>:hasChild

� Separation has no logical significance

� But may be conceptually and implementationally convenient

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DL Knowledge Base Example

� Tbox (terminology, taxonomy)

� Abox (membership assertions)

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Copyright 2009 by CEBT

Description Logic Family

� DLs are a family of logic based KR formalisms

� Particular languages mainly characterised by:

� Set of constructors for building complex concepts and roles from simpler ones

� Set of axioms for asserting facts about concepts, roles and individuals

� ALC (Attributive Language with Complements) is the smallest DL

� ALC ::= ⊥ | A | ¬C | C ∧ D | C ∨ D | ∃R.C | ∀R.C

� Constructors include booleans (and, or, not), and

� Restrictions on role successors

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Copyright 2009 by CEBT

OWL Full, DL, Lite

� SHOIQ = OWL DL

� S =ALCR+: ALC with transitive role

� H = role hierarchy

� O = nominal, e.g, WeekEnd = {Saturday, Sunday}

� I = Inverse role

� Q = qualified number restriction e.g. ≥1 hasChild.Man

– N = number restriction e.g. ≥1 hasChild

� OWL Lite = SHIF(Dn)

� F = functionality: (≤1 R)

� Complexity

� SHOIQ: NExpTime (adding transitive roles => undecidable: OWL full)

� SHIF: ExpTime

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Triple store & SPARQL

Page 18: OWL & SPARQL - SNUids.snu.ac.kr/w/images/f/f0/wec_2009_owl_sparql.pdf · Center for E-Business Technology OWL & SPARQL -22. Copyright 2009 by CEBT SPARQL SPARQL is a query language

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createTripleStore(“seminar.db" )

addTriple (Person1 first-name Steve)

addTriple (Person1 isa Organizer)

addTriple (Person1 age 52)

addTriple (Person2 first-name Jans)

addTriple (Person2 isa Psychologist)

addTriple (Person2 age 50)

addTriple (Person3 first-name Craig)

addTriple (Person3 isa SalesPerson)

addTriple (Person3 age 32)

addTriple (Person1 colleague-of Person2)

addTriple (Person1 colleague-of Person3)

addTriple (Person1 likes Pizza)

addTriple ( Person3 neighbour-of Person1)

addTriple ( Person3 neighbour-of Person2)

Triples as Graph

[Franz, Inc., 2008]

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(select (?xname ?yname)

(?x colleague-of ?y)

(?y neighbour-of ?x)

(?x first-name ?xname)

(?y first-name ?yname))

Query the Graph

[Franz, Inc., 2008]

OWL & SPARQL - 19Center for E-Business Technology

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Triple Store

� A system to provide a mechanism for persistent storage and

access of RDF graphs.

� Persistent RDF storage

� Why?

� Relational model vs OO model vs RDF model

� Everything is modeled as triples => very flexible

– cf. relational model

� Simple

– cf. relational model, OO model

� Standards –based

– cf. OO model

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Triple Store Architectures

� In memory

� Internal data representation of graph

� Will not scale

� RDB based

� Built on top of a relational DB - easy implementation

� Not optimized for RDF graph

� RDF specific

� Specially designed storage system for RDF graphs

� Optimized but New (not mature)

� AllegroGraph, Sesame, Oracle 11g (?)

� Issues

� Scalability

� Language support: SPARQL

� Level of inference: RDFS, OWL (levels), …

� Interoperability: APIs

� Relational-to-RDF mapping

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Triple Store Benchmarks

� Lehigh University Benchmark (LUBM)

� Ontology: The benchmark ontology (named Univ-Bench)

� Data Generator(UBA): Tool to generate synthetic OWL data over the Univ-Bench ontology in the unit of a university

� Test Queries: 14 test queries

� Tester (UBT) : The test module

� Ontology Benchmark (UOBM)

� extends the LUBM benchmark in terms of inference and scalability testing

� UOBM ontology and data set

� Berlin SPARQL Benchmark (BSBM)

� designed along an e-commerce use case

� SPARQL and SQL version available

� SP2Bench

� a scalable RDF data generator

� a set of benchmark queries

OWL & SPARQL - 22Center for E-Business Technology

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SPARQL

� SPARQL is a query language and a protocol for accessing RDF

� designed by the W3C RDF Data Access Working Group.

� a W3C Recommendation: SPARQL Query Language for RDF,

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

� SPARQL Query language can be used to get information from

RDF graphs.

� It provides facilities 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.

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The Semantic Web Layer Tower

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Copyright 2009 by CEBT

Basic Graph Pattern

� Triple Patterns

� Matching a triple pattern to a graph: bindings between variables

and RDF Terms

?book dc:title ?title

x v

rdf:type rdf:Property

rdf:type rdf:type rdf:Property

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

Data

Query

Query Result

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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" .

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

_:b foaf:name "Peter Guy" .

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

name mbox

"Johnny Lee " <mailto:[email protected]>

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

Data

Query

Query Result

[ Written in Turtle format:Terse RDF Triple Language ]

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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" .

:book2 ns:price 23 .

title price

"The Semantic Web" 23

Data

Query

Query Result

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 . }

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Copyright 2009 by CEBT

@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" .

:book2 ns:price 23 .

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 }}title price

“SPARQL Tutorial“

"The Semantic Web" 23

Data

Query

Query Result

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

SELECT ?name

WHERE { ?x foaf:name ?name }

ORDER BY ?name

Order By

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

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

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

SELECT ?name

WHERE { ?x foaf:name ?name ; :empId ?emp }

ORDER BY DESC(?emp)

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nameX nameY nickY

"Alice" "Bob"

"Alice" "Clare" "CT"

In XML Form

<?xml version="1.0"?>

<sparql

xmlns="http://www.w3.org/2005/sparql-

results#">

<head>

<variable name="nameX"/>

<variable name="nameY"/>

<variable name="nickY"/>

</head>

<results>

<result>

<binding name="nameX">

<literal>Alice</literal>

</binding>

[SPARQL Variable Binding Results XML Format]

<binding name="nameY">

<literal>Bob</literal>

</binding>

</result>

<result>

<binding name="nameX">

<literal>Alice</literal>

</binding>

<binding name="nameY">

<literal>Clare</literal>

</binding>

<binding name="nickY">

<literal>CT</literal>

</binding>

</result>

</results>

</sparql>

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Query forms and Extensions

� Query forms

� SELECT: returns all, or a 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

� DESCRIBE: returns an RDF graph that describes the resources found.

� ASK: returns whether a query pattern matches or not.

� Related specifications

� SPARQL Query Language for RDF

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

– defines the syntax and semantics of the SPARQL query language for RDF

� SPARQL Protocol for RDF

– http://www.w3.org/TR/rdf-sparql-protocol/

– defines the remote protocol for issuing SPARQL queries and receiving the results

� SPARQL Query Results XML Format

– http://www.w3.org/TR/rdf-sparql-XMLres/

– defines an XML document format for representing the results of SPARQL queries

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OWL & SPARQL

Center for E-Business TechnologySeoul National University

Seoul, Korea

Copyright © 2008~2009 SNU Center for E-Business Technology. All rights reserved.