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rdfjenaontologyprotege

Jena: property name cannot be resolved to a variable?

I'm using Jena to query my ontology, and I'm following Step 8: Querying a Model of this tutorial. The RDF file vc-db-1.rdf being queried here is generated from Step 3: Writing RDF and is shown below:

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:vcard="http://www.w3.org/2001/vcard-rdf/3.0#" > 
  <rdf:Description rdf:nodeID="A0">
    <vcard:Family>Smith</vcard:Family>
    <vcard:Given>John</vcard:Given>
  </rdf:Description>
  <rdf:Description rdf:about="http://somewhere/JohnSmith">
    <vcard:N rdf:nodeID="A0"/>
    <vcard:FN>John Smith</vcard:FN>
  </rdf:Description>
</rdf:RDF>

The sample code is tutorial 7 and can be downloaded here.

I noticed that in the line

ResIterator iter = model.listResourcesWithProperty(VCARD.FN);

VCARD.FN is only a property name from the RDF, but not a defined variable in my code. However, it can be successfully recognized here and the code runs without any problem.

But this is not the case with my own RDF file. I created an ontology pottery.owl with Protege and saved it in RDF/XML language. The file content is as followed:

<?xml version="1.0"?>
<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:protege="http://protege.stanford.edu/plugins/owl/protege#"
    xmlns:xsp="http://www.owl-ontologies.com/2005/08/07/xsp.owl#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:swrl="http://www.w3.org/2003/11/swrl#"
    xmlns="http://www.owl-ontologies.com/Ontology1369190090.owl#"
    xmlns:swrlb="http://www.w3.org/2003/11/swrlb#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
  xml:base="http://www.owl-ontologies.com/Ontology1369190090.owl" > 
  <rdf:Description rdf:about="">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Ontology"/>
  </rdf:Description>
  <rdf:Description rdf:about="#pottery">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Class"/>
  </rdf:Description>
  <rdf:Description rdf:about="#pottery_instance_1">
    <rdf:type rdf:resource="#pottery"/>
    <pottery.colors rdf:datatype="http://www.w3.org/2001/XMLSchema#string">blue</pottery.colors>
  </rdf:Description>
  <rdf:Description rdf:about="#pottery.colors">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#DatatypeProperty"/>
    <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#string"/>
    <rdfs:domain rdf:resource="#pottery"/>
  </rdf:Description>
</rdf:RDF>

<!-- Created with Protege (with OWL Plugin 3.4.8, Build 629)  http://protege.stanford.edu -->

The ontology contains a class pottery, an instance pottery_instance_1, and a datatype property pottery.colors.

And I modified these lines in the original code:

static final String inputFileName = "pottery.owl";
// ...
ResIterator iter = model.listResourcesWithProperty(pottery.colors);
// ...
System.out.println("  " + iter.nextResource()
                              .getProperty(pottery.colors)
                              .getString());

This time I got the error "pottery cannot be resolved to a variable."

What's the trick here? Does it have anything to do with the difference between the formats of the two RDFs? Or something else? Thank you.

Solution

  • VCARD is a java class define in package com.hp.hpl.jena.vocabulary. It contains Java constants for all the items in the (now, old) VCard vocabulary.

    If you want to generate your own class from your ontology, look at the schemagen application shipped with Jena.