Jena --- A Java API for RDF

1
Jena --- A Java API for RDF

• Jing deng
• CSCI 7818 Web Technologies
• Computer Science Department
• University of Colorado at Boulder
• Wednesday, October 31, 2001

2
Outline

• Introduction RDF and Jena
• Install and Run Jena
• Jena package and Interface
• Jena API examples
• References

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RDF

• Resource Description Framework
• represents information on Web with
  machine-understandable syntax and semantics
• Framework Subject has the predicate whose value
  is object
• Resource (Subject)
• Property (Predicate)
• Literal (Object)

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RDF (Cont.)
Tutorial
DCcreator
DCtitle

• DCdate

Oct 31 2001
Introduction
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Jena

• A Java API for RDF
• Developed by Brian McBride of HP
• Derived from SiRPAC API
• Can parse, create, and search RDF models
• Easy to use

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Install and Run Jena

• Get package from http//www.hpl.hp.co.uk/people/bw
  m/rdf/jena/download.htm
• Unzip it
• Setup environments (CLASSPATH)
• Test tutorial programs
• http//www.bmcb.btinternet.co.uk/2001/rdf/jenatuto
  rial/
• Online documentation
• http//www.hpl.hp.co.uk/people/bwm/rdf/jena/javado
  c/index.html

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Jena package

• jena.model
• Key package for application developer. It
  contains interfaces for model, resource,
• jena.mem
• Contains an implementation of Jena API which
  stores all model state in main memory
• Jena.common
• Contains implementation classes

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Jena API Structure
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Jena interfaces

• Model a set of statements
• Statement a triple of R, P, O
• Resource subject, URI
• Property item of resource
• Object may be a resource or a literal
• Literal non-nested object
• Container special resource, collection of things

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Jena interfaces (cont.)
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Ex. 1 Create Resource

• static String tutorialURI "http//hostname/rdf/t
  utorial/"
• static String author "Brian McBride"
• static String title "An Introduction to RDF and
  the Jena API"
• static String date "23/01/2001"
• Model model new ModelMem()
• Resource tutorial model.createResource(tutorialU
  RI)
• tutorial.addProperty(DC.creator, author)
• tutorial.addProperty(DC.title, title)
• tutorial.addProperty(DC.date, date)

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Ex. 2 Go through Statements

• StmtIterator iter model.listStatements()
• while (iter.hasNext())
• Statement stmt iter.next()
• Resource subject stmt.getSubject()
• Property predicate stmt.getPredicate()
• RDFNode object stmt.getObject()
• System.out.print("(" predicate.toString()
  ",")
• System.out.print(" " subject.toString()
  ",")
• if (object instanceof Resource)
• System.out.print(" " object.toString())
• else
• System.out.print(" \"" object.toString()
  "\"") System.out.println(")")

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Ex. 3 Read and Write File

• Model model new ModelMem()
• String filename temp/tutorial4.xml
• Model.read(new FileReader(filename), )
• Model.write(new PrintWriter(System.out))
• // or
• String output_filename temp/test.xml
• Model.write(new PrintWriter(new
  FileOutputStream(output_filename)))

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Ex. 4 Navigating a Model

• Property email model.createProperty(tutorialURI,
  "emailAddress")
• Resource tutorial model.getResource(tutorialURI)
  
• Resource author tutorial.getProperty(DC.creator)
  .getResource()
• StmtIterator iter author.listProperties(email)
  
• while (iter.hasNext())
• System.out.println(" " iter.next().getObject().
  toString())

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Ex. 5 Querying a Model

• ResIterator iter model.listSubjectsWithProperty(
  DC.date, date)
• while (iter.hasNext())
• cout ltlt iter.next().getProperty(DC.title)
  .getString()
• NodeIterator iter2 model.listObjectsOfProperty(D
  C.creator)
• while (iter2.hasNext())
• cout ltlt ((Resource)iter2.next())
  .getProperty(name) .getString()

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Containers

• Represents collections of things
• BAG unordered collection
• ALT unordered collection except first element
• SEQ ordered collection

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Ex. 6 Containers

• Bag bag model.createBag()
• bag.add("Romeo and Juliet")
• .add("Hamlet")
• .add("Othello")
• NodeIterator iter bag.iterator()
• while (iter.hasNext())
• System.out.println(" " iter.next().toString())
  
• model.write(new PrintWriter(System.out))

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References

• Jena Web Site
• http//www.hpl.hp.co.uk/people/bwm/index.html
• Jena tutorial
• http//bmcb.btinternet.co.uk/2001/rdf/jenatutorial
  /
• http//www.xml.com/pub/a/2001/05/23/jena.html
• RDF Model and Syntax Specification
• http//www.w3.org/TR/1999/REC-rdf-syntax-19990222/

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Thanks!