5 Replies Latest reply on Jan 22, 2015 6:37 PM by alwu-Oracle

blank nodes and describe queries

M.R. Strand Nov 27, 2014 3:47 PM

I am unable to make a post containing my problem. I get a message stating that "Due to span, this content is blocked".

When I removed the examples, it worked. I dont know what example triggered your spam filter though. Hopefully the below text makes sense even without the examples.

--- Trying here again: Removing all examples. .

On other implementations of the SPARQL protocol, (i.e. Jenas TDB), a DESCRIBE query will return a model containing.

1. The subject resource

2. All resources connected to the subject with any property.

3. If the resource found in (2) is a blank node, repeat (1) with that blank node as subject.

Unless: A describe of that blank node has been done before.

This ensures that blank nodes are usefull when using describe. If this is not the case, the resulting model is useless. For instance, we get the following answer (prefixes omitted)

As you can see, the complex OWL restrictions, which uses blank nodes, are omitted.

The same query using SEM MATCH, gives me, among other things, this line:

I realize we can use this to create a PL/SQL method that iteratively builds a set of triples by following the bnodes, but I trust Oracle over myself to write that function efficiently.

Is this something you are aware of and fixing, or will the task fall to me?

Br,

Morten

1. Re: blank nodes and describe queries

alwu-Oracle Dec 1, 2014 5:58 PM (in response to M.R. Strand)

Hi Morten,

Sorry about the trouble with posting your question on OTN.

Can you please email me the output?

Thanks,

Zhe Wu
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2. Re: blank nodes and describe queries

alwu-Oracle Dec 1, 2014 9:19 PM (in response to M.R. Strand)

Hi Morten,

I did a quick test. I created a small ontology (using Protege and Oracle's Protege plugin) which has the following class expression for concept D. Basically, D is a subclass of the intersection of class A and the union of class B and class C.
There are quite a few bNodes involved in this expression.

D SubClassOf    A and (B or C)

From both Joseki and Fuseki, I can get the following correct output for this query "DESCRIBE <http://www.co-ode.org/ontologies/ont.owl#D>"

<rdf:RDF>
   <owl:Class rdf:about="http://www.co-ode.org/ontologies/ont.owl#D">
       <rdfs:subClassOf>
           <owl:Class>
                <owl:intersectionOf rdf:parseType="Collection">
                    <rdf:Description rdf:about="http://www.co-ode.org/ontologies/ont.owl#A"/>
                     <owl:Class>
                           <owl:unionOf rdf:parseType="Collection">
                               <rdf:Description rdf:about="http://www.co-ode.org/ontologies/ont.owl#B"/>
                               <rdf:Description rdf:about="http://www.co-ode.org/ontologies/ont.owl#C"/>
                           </owl:unionOf>
                    </owl:Class></owl:intersectionOf></owl:Class></rdfs:subClassOf></owl:Class></rdf:RDF>

Hope it helps,

Zhe Wu
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3. Re: blank nodes and describe queries

M.R. Strand Jan 5, 2015 1:22 PM (in response to alwu-Oracle)

I got it working on a normal model. However, when I tried it on a virtual model it failed.

Could you try to wrap the model you had above in a virtual model and see if you still get correct results?

Thank you!
Morten
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4. Re: blank nodes and describe queries

alwu-Oracle Jan 7, 2015 5:33 PM (in response to M.R. Strand)

Hi Morten,

I did reproduce the problem with a virtual model. Thanks! The problem is that when querying a blank node as a resource (not as an existential), we need to prefix the bNode label with the model ID. If we are using a regular model, we have the correct model ID. When a virtual model is used, we no longer have the correct model ID.

Please file an SR.

Thanks,

Zhe Wu
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5. Re: blank nodes and describe queries

alwu-Oracle Jan 22, 2015 6:37 PM (in response to M.R. Strand)

Hi Morten,

This problem has been fixed. Please check the SR. Jorge has already updated it.

Thanks,

Zhe
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