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

3. 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)

4. RDF (Cont.) Tutorial Oct 31 2001Introduction DC:creator DC:dat e DC:title Brain @hotmail @yahoo Tut:name Tut:email

5. 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

6. Install and Run Jena Get package from http://www.hpl.hp.co.uk/people/bwm/rdf/jena/ download.htm http://www.hpl.hp.co.uk/people/bwm/rdf/jena/ download.htm Unzip it Setup environments (CLASSPATH) Test tutorial programs –http://www.bmcb.btinternet.co.uk/2001/rdf/jenatuto rial/http://www.bmcb.btinternet.co.uk/2001/rdf/jenatuto rial/ Online documentation –http://www.hpl.hp.co.uk/people/bwm/rdf/jena/javad oc/index.htmlhttp://www.hpl.hp.co.uk/people/bwm/rdf/jena/javad oc/index.html

7. 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

8. Jena API Structure

9. 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

10. Jena interfaces (cont.) Tutorial Oct 31 2001Introduction DC:author DC:date DC:title Brain @hotmail @yahoo Tut:name Tut:email Model Statement resource property Literal object

11. Ex. 1 Create Resource static String tutorialURI = "http://hostname/rdf/tutorial/"; 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(tutorialURI); tutorial.addProperty(DC.creator, author); tutorial.addProperty(DC.title, title); tutorial.addProperty(DC.date, date);

12. 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(")"); }

13. 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)));

14. 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()); }

15. Ex. 5 Querying a Model ResIterator iter = model.listSubjectsWithProperty(DC.date, date); while (iter.hasNext()) { cout << iter.next().getProperty(DC.title).getString(); } NodeIterator iter2 = model.listObjectsOfProperty(DC.creator); while (iter2.hasNext()) { cout << ((Resource)iter2.next()).getProperty(name).getString(); }

16. Containers Represents collections of things –BAG : unordered collection –ALT: unordered collection except first element –SEQ: ordered collection

17. 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));

18. References Jena Web Site –http://www.hpl.hp.co.uk/people/bwm/index.htmlhttp://www.hpl.hp.co.uk/people/bwm/index.html Jena tutorial –http://bmcb.btinternet.co.uk/2001/rdf/jenatutorial/http://bmcb.btinternet.co.uk/2001/rdf/jenatutorial/ –http://www.xml.com/pub/a/2001/05/23/jena.htmlhttp://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/http://www.w3.org/TR/1999/REC-rdf-syntax- 19990222/

19. Thanks!