Jena 101

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Contents 1 Jena Introduction 1.1 how to install 1.2 Jena programming basics 1.3 Ontology and Inference 1.4 advanced topics 2 Exercises 2.1 RDF Syntax converter 2.2 RDF graph summary 2.3 OWL ontology summary 2.4 RDF loader 2.5 OWL form generator

Jena Introduction

The content in this section is mainly based on Jena Home Page

A few facts about jena

• Jena is a JAVA toolkit for Semantic Web applications
  • parse, validate and write RDF documents in various formats
  • RDF data access API (in-memory and database backend)
  • support SPARQL query
  • support RDFS reasoning and some kinds of OWL reasoning
• Jena is open source maintained by HP Labs

how to install

1. install JAVA, e.g. sun J2SE 1.5
2. [optional] download and install eclipse IDE if you prefer GUI JAVA programming
3. download jena most recent release (v2.5.4 as of Oct 2007) from http://jena.sourceforge.net/downloads.html
4. build a java project and include all libs under JENAHOME/lib in your java classpath.

Jena programming basics

An Introduction to RDF and the Jena RDF API

• Model, Statement, Resource, Literal, URIResource, Property
• "RDF/XML", "RDF/XML-ABBREV", "N-TRIPLE", "N3"
• read, write, query, createDefaultModel, setNsPrefix

   read
   write
   listStatement
   listSubjectWithProperty

Jena I/O Mini HowTo

• xml prolog, character encoding (mainly based on Sun J2SE)
• override RDFReader to intercept parsing errors

Ontology and Inference

Jena 2 Ontology API

• create ontology model

   OntModel m = ModelFactory.createOntologyModel( OntModelSpec.RDFS_MEM );
   setProcessImports( false ) 

• OntResoure, OntClass, OntProperty
• Caching

   setCacheModels( boolean caching )
   
   OntModel m = ModelFactory.createOntologyModel();
   OntDocumentManager dm = m.getDocumentManager();
   dm.addAltEntry( "http://www.xfront.com/owl/ontologies/camera/",
                   "file:" + JENA + "src-examples/data/camera.owl"    );
   m.read( "http://www.xfront.com/owl/ontologies/camera/" );

Jena 2 Inference support

• validation (OWL validation may take longer)

   Model data = FileManager.get().loadModel(fname);
   InfModel infmodel = ModelFactory.createRDFSModel(data);
   ValidityReport validity = infmodel.validate();
   if (validity.isValid()) {    
       System.out.println("OK");
   } else {
       ...

• variations of RDFS and OWL Inference
• Advanced: rule based inference, inference models

advanced topics

• Jena2 Database Interface - How To Create Persistent Models
• SPARQL Tutorial

Exercises

RDF Syntax converter

• translate from/to RDF/XML, N3, NTriples, Turtle
• make it an online service
• [optional] render parsing errors if the input file was not correct
• [optional] compare it with at least one RDF tool other than Jena

RDF graph summary

• summarize an RDF graph, e.g. "how many node, arc, and degree distribution of node"
• scalability test

OWL ontology summary

• summarize an RDF graph using RDFS/OWL inference, e.g. "given an RDF graph, list classes, properties, and instances, and show how many triples were used to describe each of them"
• render an ontology and its summary in human readable manner (e.g. text/html)

RDF loader

• load an RDF graph from file or URL, print as much as possible metadata
• generate scalability performance report on loading RDF data, show statistics and bottleneck
• [optional] compare it with at least one RDF tool other than Jena

OWL form generator

• generate a HTML form for a given class using a given RDF graph consisting both ontology and instance data
• if the form is a property-value sheet, try to fill with applicable properties and property-values (maybe in drop list)
• you may use ontology specification to generate the form, or use the usage examples from similar instance data