Question

I’m using jena 2.6.4, and I notice a strange behavior with namespaces. I’m using the following code:

public static void main(String[] args) {
    String myUri = "http://www.example.com/1.0/myUri#";
    OntModel model = ModelFactory.createOntologyModel(OntModelSpec.OWL_MEM);

    model.setNsPrefix("myuri", myUri);

    OntClass c616 = model.createClass(myUri + "616");
    OntClass c123 = model.createClass(myUri + "123");

    Individual a = c616.createIndividual(myUri + "a");
    a.addOntClass(c123);

    model.write(System.out);
}

The output is:

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:j.0="http://www.example.com/1.0/myUri#616"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:j.1="http://www.example.com/1.0/myUri#123"
    xmlns:myuri="http://www.example.com/1.0/myUri#"
    xmlns:owl="http://www.w3.org/2002/07/owl#" > 
  <rdf:Description rdf:about="http://www.example.com/1.0/myUri#123">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Class"/>
  </rdf:Description>
  <rdf:Description rdf:about="http://www.example.com/1.0/myUri#a">
    <rdf:type rdf:resource="http://www.example.com/1.0/myUri#123"/>
    <rdf:type rdf:resource="http://www.example.com/1.0/myUri#616"/>
  </rdf:Description>
  <rdf:Description rdf:about="http://www.example.com/1.0/myUri#616">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Class"/>
  </rdf:Description>
</rdf:RDF>

I don’t understand why the following namespaces are declared:

xmlns:j.0="http://www.example.com/1.0/myUri#616"
xmlns:j.1="http://www.example.com/1.0/myUri#123"

Strangely, If I change the serialization to TURTLE (model.write(System.out, "TURTLE");), then I get the following output:

@prefix myuri:   <http://www.example.com/1.0/myUri#> .
@prefix owl:     <http://www.w3.org/2002/07/owl#> .
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix xsd:     <http://www.w3.org/2001/XMLSchema#> .
@prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#> .

<http://www.example.com/1.0/myUri#123>
      a       owl:Class .

myuri:a
      a       <http://www.example.com/1.0/myUri#123> , <http://www.example.com/1.0/myUri#616> .

<http://www.example.com/1.0/myUri#616>
      a       owl:Class .

Where namespaces declarations are as I expected.

I’ve also noticed I different behavior when changing OntClass names from 616 to c616 and 123 to c123:

public static void main(String[] args) {
    String myUri = "http://www.example.com/1.0/myUri#";
    OntModel model = ModelFactory.createOntologyModel(OntModelSpec.OWL_MEM);

    model.setNsPrefix("myuri", myUri);

    OntClass c616 = model.createClass(myUri + "c616");
    OntClass c123 = model.createClass(myUri + "c123");

    Individual a = c616.createIndividual(myUri + "a");
    a.addOntClass(c123);

    model.write(System.out);
}

outputs:

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:myuri="http://www.example.com/1.0/myUri#"
    xmlns:owl="http://www.w3.org/2002/07/owl#" > 
  <rdf:Description rdf:about="http://www.example.com/1.0/myUri#c123">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Class"/>
  </rdf:Description>
  <rdf:Description rdf:about="http://www.example.com/1.0/myUri#a">
    <rdf:type rdf:resource="http://www.example.com/1.0/myUri#c123"/>
    <rdf:type rdf:resource="http://www.example.com/1.0/myUri#c616"/>
  </rdf:Description>
  <rdf:Description rdf:about="http://www.example.com/1.0/myUri#c616">
    <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Class"/>
  </rdf:Description>
</rdf:RDF>

and in TURTLE format:

@prefix myuri:   <http://www.example.com/1.0/myUri#> .
@prefix owl:     <http://www.w3.org/2002/07/owl#> .
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix xsd:     <http://www.w3.org/2001/XMLSchema#> .
@prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#> .

myuri:c123
      a       owl:Class .

myuri:a
      a       myuri:c123 , myuri:c616 .

myuri:c616
      a       owl:Class .

Am I doing something wrong? Can someone explain this strange behavior?
Thanks!

Answer 1

The two prefixes are not used and do not affect the ‘nature’ of your RDF graph.
The so called ‘localnames’ cannot start with a number, see:

• http://www.w3.org/TR/REC-xml/#NT-Name
• http://www.w3.org/TR/REC-xml/#NT-NameStartChar

The two prefixes in your first example (j.0 and j.1) are not actually used, why they concern you so much?