Re: Simple Pizza Query

[Dave Reynolds]

On 13/04/12 21:36, Andrés Zules wrote:
2012/4/10 Dave Reynolds<dave.e.reyno...@gmail.com>
On 10/04/12 16:09, Andrés Zules wrote:

  2012/4/10 Dave Reynolds<dave.e.reynolds@**gmail.com<dave.e.reyno...@gmail.com>

Well that ontology is a bit painful to work with at the SPARQL level but
you could query for (untested example):

SELECT * WHERE
{
    ?pizza rdfs:subClassof [
        owl:onProperty pizza:hasTopping;
        owl:someValuesFrom pizza:MushroomTopping ] .
}

Dave


Thanks Dave ... I realize on protege and jena this query:

SELECT *
WHERE {
?X ?Y pizza:MushroomTopping  .
}

See outputs
https://plus.google.com/photos/116190906023059719803/albums/5730984081208355185

Like I say, for that ontology as I see it when I download it then there 
should not be any matches for the query with ?Y = pizza:hasTopping.

I infer that

| _:b2                   | owl:someValuesFrom
   |
| _:b5                   | owl:someValuesFrom
   |
| _:b6                   | owl:someValuesFrom
   |
| _:b7                   | owl:someValuesFrom
   |

and

  DefaultOWLNamedClass(
http://www.co-ode.org/ontologies/pizza/pizza.owl#FourSeasons)
DefaultOWLObjectProperty(
http://www.co-ode.org/ontologies/pizza/pizza.owl#hasTopping) etc etc etc

are the pizzas with MushroomTopping

Why does Jena return _:b* and no return the names? I dont understan why the
results have differences

If you look at the declarations of the relevant Named Classes you see 
things like:

<owl:Class rdf:about="#FourSeasons">
  <rdfs:label xml:lang="pt">QuatroQueijos</rdfs:label>
  <rdfs:subClassOf>
    <owl:Restriction>
      <owl:onProperty rdf:resource="#hasTopping"/>
      <owl:someValuesFrom rdf:resource="#MushroomTopping"/>
    </owl:Restriction>
  </rdfs:subClassOf>
  ...

Putting that in Turtle to make in clearer:

  pizza:FourSeasons a owl:Class;
    rdfs:label "QuatroQueijos"@pt;
    rdfs:subClassOf [
      a owl:Restriction;
      owl:onProperty pizza:hasTopping;
      owl:someValuesFrom pizza:MushroomTopping;
    ]
    ...

So each OWL restriction is represented by a blank-node (an RDF resource 
which has no URI). If we want to write that out as a set of separate 
triples then you see:

  pizza:FourSeasons a owl:Class .
  pizza:FourSeasons rdfs:label "QuatroQueijos"@pt .
  pizza:FourSeasons rdfs:subClassOf _:b .

  _:b  a owl:Restriction .
  _:b  owl:onProperty pizza:hasTopping .
  _:b  owl:someValuesFrom pizza:MushroomTopping .

The notation _:X is what Turtle uses to represent such blank nodes, 
which is what you are seeing in Jena's output.

So all that's happening is that your query is matching the 
owl:someValuesFrom part of those restrictions, i.e. the final triple in 
the above example.  Hence my suggested query quoted above.

Dave