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[protege-owl] how to query an owl ontology

Thomas Russ tar at ISI.EDU
Wed May 21 10:27:58 PDT 2008


On May 21, 2008, at 4:36 AM, James Howison wrote:

>
> On May 20, 2008, at 7:13 PM, Martin O'Connor wrote:
>
>> anuj kumar wrote:
>>
>>> SPARQL is used to query RDF , so does that mean OWL is first
>>> converted
>>> to an RFD representation while implementing SPARQL queries with jena
>>> and since RDF is not as rich as OWL we don't get good results using
>>> SPARQL with OWL. Is my understanding correct?
>>
>> Yes. When applied to OWL, SPARQL is typically used to query the
>> serialized RDF representation of an OWL ontology. This is problematic
>> because this serialization can be extremely complex and is not
>> deterministic.
>
> Thanks, this is interesting.  I had thought that the RDF
> representation of OWL was deterministic and that SPARQL against a
> 'fully-reasoned' model, while not always as convenient as one would
> want, was at least fully capable.  Are there any resources around that
> explain the non-determinacy of OWL as RDF?

Well, I suppose in a strictly technical sense, the serialization of  
OWL into RDF is deterministic, in that a given program will always  
produce the same serialization for a given ontology.  But any change  
to the ontology can result in a radically different serialization, so  
that it is not trivially predictable.

Part of this is related to options available in the serialized form of  
OWL.  For example, the following are both valid serializations of  
"Fred is a Person":

<Person rdf:id="Fred"/>

<owl:Thing rdf:about="#Fred">
   <rdf:type rdf:resource="#Person">
</owl:Individual>

But working on the RDF, you would have to use different SPARQL queries  
to get the semantic results you would expect if you wanted to get all  
of the instances of Person.






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