On 27/10/13 10:11, Bumper Guard wrote:
Greetings!
I want to list all superclasses of a class using the
listSuperClasses()-Method of OntClass. For most classes that's not a
problem, but in some special cases I just receive a null as a
superclass. For example I've got this ontology:
...
<!-- [..]#Student -->
<Class rdf:about="[..]#Student">
<rdfs:subClassOf rdf:resource="[..]#Person"/>
<rdfs:subClassOf>
<Class>
<unionOf rdf:parseType="Collection">
<rdf:Description rdf:about="[..]#Man"/>
<rdf:Description rdf:about="[..]#Woman"/>
</unionOf>
</Class>
</rdfs:subClassOf>
</Class>
...
The [..] are just to shorten the ontology reference which is definitely
correct. The Person is recognized without any problem, but whenever the
ontology contains a "<rdfs:subClassOf> ... </rdfs:subClassOf>", it won't
find the superclass and returns null instead (ontClass.hasSuperClass()
returns true though). There are not only unions but also restrictions in
this form, that can't be found.
How can I correctly read these superclasses, whenever I receive a null?
Without seeing your code it is hard to be sure what you mean by "null".
Those classes (unions, restrictions) are anonymous (i.e. they are bNodes
and have no URI). listSuperClasses will return an OntClass for those
just fine and you can then use methods like isUnionClass, isRestriction
etc to understand what class you have and then asUnionClass etc to get
convenience methods to access the information on those classes.
You may be seeing "null" as a result of doing something like getURI or
getLocalName. Since those resources have no URI such methods should
return null.
Somewhere there is an example showing how to traverse a class hierarchy
using the Ont API which clarifies this but I can't find it in the new
web site layout.
Dave
