Introduction Semantic Web technologies Jena
Jena – A Semantic Web Framework for Java
Aleksander Pohl
Katedra Informatyki, Akademia Górniczo-Hutnicza
2. luty 2009
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Agenda
Introduction
Semantic Web technologies
Jena
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Agenda
Introduction
Semantic Web technologies
Jena
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
What is the Semantic Web?
The Semantic Web is an:
... extension of current web in which
◮
... information is given well defined meaning
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... better enabling people and computers to work in
◮
cooperations.
The Semantic Web, Tim Barners-Lee, James Hendler and Ora
Lassil
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Motivation
providing information about Web resources and the
◮
systems that use them
allowing data to be processed outside the particular
◮
environment in which it was created
combining data from several applications to arrive at new
◮
information
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Agenda
Introduction
Semantic Web technologies
Jena
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Core Semantic Web technologies
RDF – Resource Description Framework
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RDFS – RDF Schema (vocabulary)
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OWL – Web Ontology Language
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SPARQL – Query Language for RDF
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Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDF – Resource Description Framework
based on XML and URIs
◮
directed, labeled graph format for representing
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information in the web
formal semantics allows well founded deductions in RDF
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data
extensible vocabulary
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Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDF – graph data model
any expression in RDF is a collection of triples
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every triple consists of a subject, a predicate and an object
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the arc direction is significant – it always points toward the
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object
assertion of an RDF triple says that some relationship,
◮
indicated by the predicate, holds between the things
denoted by subject and object of the triple
meaning of an RDF graph is the conjunction (logical AND)
◮
of the statements corresponding to all the triples it contains
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDF – subject, predicate & object
nodes of an RDF graph are its subjects and objects
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a node may be:
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URI with optional fragment identifier, eg.
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http://www.example.org/staffid/1234#xyz
literal, eg. \"George\"
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blank
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the subject of a triple might be only URI reference or
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a blank node
the predicate of the triple must be URI reference
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Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDF – example
<rdf:Description rdf:about=\"http://www.ivan-herman.net\">
<foaf:name>Ivan</foaf:name>
<abc:myCalendar rdf:resource=\"http://.../myCalendar\"/>
<foaf:surname>Herman</foaf:surname>
</rdf:Description>
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDFS – RDF Vocabulary Description Language
RDF itself provides no means for defining
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application-specific classes and properties
They are described in RDFS – RDF Vocabulary
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Description Language (aka RDF Schema)
RDF Schema provides a type system for RDF, similar to
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type systems in programming languages:
allows resources to be defined as instances of one or more
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classes
allows classes to be organized in a hierarchical fashion
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URIref prefix
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http://www.w3.org/2000/01/rdf-schema#,
conventionally associated with the QName prefix rdfs:
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDFS – basic notions (1)
Classes are described using the RDFS resources:
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rdfs:Class
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rdfs:Resource
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and the properties:
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rdf:type
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rdfs:subClassOf
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Example:
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ex:MotorVehicle rdf:type rdfs:Class.
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Java: class MotorVehicle {· · · }
exthings:myCar rdf:type ex:MotorVehicle.
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Java: myCar = new MotorVehicle();
ex:Van rdfs:subClassOf ex:MotorVehicle.
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Java: class Van extends MotorVehicle {· · · }
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
OWL – Web Ontology Language
Intended to be used when the information needs to be
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processed by applications (not merely presented to
humans)
Provides additional vocabulary along with a formal
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semantics
Sublanguages:
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Lite – classification hierarchy and simple constraints
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(extension of restricted RDF)
DL (Description Logic) – maximum expressiveness while
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retaining computational completeness (extension of
restricted RDF)
Full – maximum expressiveness and the syntactic freedom
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of RDF with no computational guarantees (real extension of
RDF)
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
OWL Lite additions
(In)Equality: equivalentClass,
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equivalentProperty, sameAs, differentFrom, ...
Property characteristics: inverseOf,
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TransitiveProperty, SymmetricProperty, ...
Restricted Cardinality: minCardinality,
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maxCardinality, cardinality
Annotation Properties: rdfs:label, rdfs:comment,
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rdfs:seeAlso, rdfs:isDefinedBy,
AnnotationProperty, OntologyProperty
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Semantic Web – ontologies overview
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
SPARQL – overview
SPARQL is a query language for RDF
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It is similar to SQL in terms of purpose and syntax, but
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different in terms of application (relational data vs. graph
based data)
Human-friendly syntax
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Data integration and aggregation – multiple sources
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supported by default
Allows to make yes/no questions
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Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
SPARQL Example
Data:
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<http://example.org/book/book1>
<http://purl.org/dc/elements/1.1/title>
”SPARQL Tutorial” .
Query:
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SELECT ?title WHERE {
<http://example.org/book/book1>
<http://purl.org/dc/elements/1.1/title>
?title . }
Result:
◮
title
”SPARQL Tutorial”
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Agenda
Introduction
Semantic Web technologies
Jena
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Jena2 – overview
Developed by HP Laboratories
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Open-source Java implementation of core Semantic Web
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technologies:
RDF graph manipulation API
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RDFS and OWL reasoning API
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Includes the de facto reference RDF/XML parser
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RDF/XML, N3 and N-triple Input/Output
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SPQRQL query engine
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rule-based inference engine
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In-memory or persistent storage
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Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
RDF API example
// some definitions
1
static String personURI = \"http://somewhere/JohnSmith\";
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static String fullName = \"John Smith\";
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4
// create an empty Model
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Model model = ModelFactory.createDefaultModel();
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// create the resource
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Resource johnSmith = model.createResource(personURI);
9
10
// add the property
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johnSmith.addProperty(VCARD.FN, fullName);
12
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
SPARQL API example
Model model = ... ;
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String queryString = \" .... \" ;
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Query query = QueryFactory.create(queryString) ;
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QueryExecution qexec = QueryExecutionFactory.create(query, model) ;
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try {
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ResultSet results = qexec.execSelect() ;
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for ( ; results.hasNext() ; )
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{
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QuerySolution soln = results.nextSolution() ;
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// Get a result variable by name.
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RDFNode x = soln.get(\"varName\") ;
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// Get a result variable - must be a resource
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Resource r = soln.getResource(\"VarR\") ;
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// Get a result variable - must be a literal
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Literal l = soln.getLiteral(\"VarL\") ;
15
}
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} finally { qexec.close() ; }
17
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Jena comparison
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Bibliography (1)
Brickley, Dan; Guha, Ramanathan (2004). RDF Vocabulary
◮
Description Language 1.0: RDF Schema,
http://www.w3.org/TR/rdf-schema/
Carroll, Jeremy J.; Dickinson, Ian; Dollin, Chris; Reynolds,
◮
Dave; Seaborne, Andy; Wilkinson, Kevin (2003). Jena:
Implementing the Semantic Web Recommendations, HP
Laboratories, Bristol, technical report HPL-2003-146.
Herman, Ivan Questions (and Answers) on the semantic
◮
Web, http://www.w3.org/People/Ivan/-
CorePresentations/SW_QA
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java

Introduction Semantic Web technologies Jena
Bibliography (2)
Klyne, Graham; Carroll, Jeremy J. (2004). Resource
◮
Description Framework (RDF): Concepts and Abstract
Syntax http://www.w3.org/TR/rdf-concepts/
McBride, Brian (2002), The Semantic Web, HP
◮
Laboratories, Bristol, Euroweb 2002 invited talk.
McGuinness, Deborah; van Harmelen, Frank (2004). OWL
◮
Web Ontology Language Overview,
http://www.w3.org/TR/owl-features/
Aleksander Pohl KI AGH
Jena – A Semantic Web Framework for Java