[Pellet-users] Inferred Subsumption
JPQ
jpq.semantics at gmail.com
Fri Mar 7 19:55:18 UTC 2008
Evren,
Thanks for the reply; it sheds new light on my understanding of OWL.
Basically, OWL describes classes in one of two ways:
1. A named (ie, Type-1) class, which is formed from the <owl:Class>
construct, including a URI reference
2. An unnamed (ie, anonymous) class, which is formed from the
<owl:Class> construct and lacks a URI reference
As for class descriptions:
1. A class identifier is defined by point 1 above
2. An enumeration contains a list of invidividuals. Lacking other
class description types, a class (named or anonymous) having an enumeration
class description means its class extension has EXACTLY those individuals
and no others.
3. A property restriction defines value and cardinality constraints.
Lacking other class description types, a class (named or anonymous) having
property restrictions means its class extension must adhere to the value and
cardinality "rules" described by the restrictions, and these "rules" are
local to the class.
4. Class descriptions 4-6 (the set operations) limit the selection of
individuals from other classes described in the set operations. Lacking
other class description types, a class (named or anonymous) utilizing set
operations means its class extension is EXACTLY described by individuals of
other classes that meet the criteria of the set operations.
If this is an accurate description, then it is clear that class equivalency
can ONLY be established through the <owl:equivalentClass> construct. In
fact, this can be demonstrated in TopBraid Composer with the following
example.
1. Create a named class, and define a union set operation only.
2. Select the class in the "Classes" pane, and then switch over to the
"Diagram" view. The union operation does not displayed, because it does not
signify a class.
3. Modify the named class as follows.
1. Wrap the union operation in an anonymous class
2. Wrap the anonymous in <owl:equivalentClass>
4. Save the file
5. Select the named class in the "Classes" pane; switch to the
"Diagram" view. The union operation is not displayed inside a gray box. The
gray box signifies an anonymous class. There is an equivalency relation (ie,
a thick double-head black arrow) drawn between the anonymous class (ie, the
gray box) and the named class.
On 3/6/08, Evren Sirin <evren at clarkparsia.com> wrote:
> [Note: please send Pellet questions to the mailing list not privately]
>
> On 3/5/08 2:26 PM, JPQ wrote:
> > As a follow-up to my last post, a recent discussion elsewhere suggested
> that
> > Pellet does not return inferences on blank nodes. This would explain why
> > Pellet infers a subsumption and not an equivalency. More specifically,
> here
> > is what Pellet returns in Topbraid Composer.
> >
> > Another_Ontology:Lat rdfs:subClassOf LatLon
> > Another_Ontology:Lon rdfs:subClassOf LatLon
> >
> > I accepted to see the following inference, also.
> >
> > LatLon rdfs:subClassOf
> > [Another_Ontology:Lat or Another_Ontology:Lon]
> >
> > These inferences collectively describe the equivalency between "LatLon"
> and
> > "[Another_Ontology:Lat or Another_Ontology:Lon]".
> >
>
> In you snippet there is no blank node that describes the union class. If
> your definition was written as follows (using an anonymous class for the
> union description):
>
> <owl:Class rdf:ID="LatLon">
> <owl:equivalentClass>
> <owl:Class>
> <owl:unionOf rdf:parseType="Collection">
> <rdf:Description rdf:about="Another_Ontology.owl#Lat"/>
> <rdf:Description rdf:about="Another_Ontology.owl#Lon"/>
> </owl:unionOf>
> </owl:Class>
> </owl:equivalentClass>
> </owl:Class>
>
> then you would get a bnode in the inferences (but Jena will not pretty
> print the bnode in the Manchester syntax you have above). Also note that
> Pellet will only return asserted relations regarding bnodes. See this
> FAQ entry for more information [1].
>
> If you are interested in seeing why the subclass relation holds then you
> can take a look at the explanation feature Pellet provide. Pellet will
> give you the set of asserted axioms for a given inference. See the
> explanation example program from Pellet distribution.
>
> Cheers,
> Evren
>
> [1] http://pellet.owldl.com/faq/different-results/
>
>
> > On 3/4/08, JPQ <jpq.semantics at gmail.com> wrote:
> >
> >> Thanks for your reply.
> >>
> >> Let me phrase it a bit differently.
> >>
> >> First, we have the following OWL class, which is contained within an
> >> OWL-DL ontology. In fact this ontology only contains this one class and
> no
> >> properties. Additionally, it imports a second ontology, which I have
> called
> >> "Another_Ontology".
> >>
> >> <owl:Class rdf:ID="LatLon">
> >> <owl:unionOf rdf:parseType="Collection">
> >> <rdf:Description rdf:about="Another_Ontology.owl#Lat"/>
> >> <rdf:Description rdf:about="Another_Ontology.owl#Lon"/>
> >> </owl:unionOf>
> >> </owl:Class>
> >> The named OWL class, "LatLon", is equivalent to the nested anonymous
> class
> >> that is formed by the "unionOf" set operator. For example, suppose the
> class
> >> extension of "Lat" is represent by the set {1, 2, 3}, and the class
> >> extension of "Lon" is represented by the set {4, 5, 6}. Then the class
> >> extension of "LatLon" is exactly the same as the union of those two
> sets -
> >> namely, {1,, 2, 3, 4, 5, 6}.
> >>
> >> Yet, when run through Pellet, it is inferred that
> >> "Another_Ontology.owl#Lat" & "Another_Ontology.owl#Lon" are subclasses
> of
> >> "LatLon".
> >>
> >> My question is what is the basis of these inferences?
> >>
> >> Thanks.
> >>
> >> On 3/4/08, Evren Sirin <evren at clarkparsia.com> wrote:
> >>
> >>> On 3/4/08 11:51 AM, JPQ wrote:
> >>>
> >>>> I'm running the Pellet inferencing engine in TopBraid Composer on a
> >>>>
> >>> valid
> >>>
> >>>> OWL-DL document. Here are the details.
> >>>>
> >>>> An OWL-DL ontology contains the following class.
> >>>> <owl:Class rdf:ID="LatLon">
> >>>> <owl:unionOf rdf:parseType="Collection">
> >>>> <rdf:Description rdf:about="Another_Ontology.owl#Lat"/>
> >>>> <rdf:Description rdf:about="Another_Ontology.owl#Lon"/>
> >>>> </owl:unionOf>
> >>>> </owl:Class>
> >>>>
> >>>> The anonymous class formed by the "unionOf" set operation is
> >>>>
> >>> equivalent to
> >>>
> >>>> the named class, "LatLon".
> >>>>
> >>>> This ontology imports a second ontology.
> >>>>
> >>>> The second OWL-DL ontology ("Another_Ontology") has the following
> >>>>
> >>> features:
> >>>
> >>>> 1. The "Lat" & "Lon" classes are Type-1 OWL classes (ie, they are
> >>>>
> >>> simply
> >>>
> >>>> identified as RDF nodes using the rdf:ID construct)
> >>>> 2. There exist "lat" & "lon" datatype properties
> >>>> a. The "lat" property domain is "Lat"; its range is "xsd:double".
> >>>>
> >>> The
> >>>
> >>>> same applies with "lon",
> >>>> except its domain is "Lon".
> >>>> (I've also tried an alternate version where the "lat" & "lon"
> >>>> datatype properties only define
> >>>> ranges and not domains.)
> >>>>
> >>>> b. Both the "lat" & "lon" datatype properties are also typed with
> >>>> <owl:FunctionalProperty>
> >>>>
> >>>> Running the Pellet inference engine on the first ontology results in
> >>>>
> >>> the
> >>>
> >>>> following inferences.
> >>>> Another_Ontology:Lat rdfs:subClassOf LatLon
> >>>> Another_Ontology:Lon rdfs:subClassOf LatLon
> >>>>
> >>>> The "LatLon" class subsumes "Lat" & "Lon".
> >>>>
> >>>>
> >>> Ok, everything sounds right until now.
> >>>
> >>>
> >>>> Why does Pellet infer these subsumptions when the "LatLon" class
> >>>>
> >>> description
> >>>
> >>>> defines an equivalency?
> >>>>
> >>>>
> >>> I don't understand the question or the problem. Are you saying that
> the
> >>> subclass relations do not hold when you change the definition of
> LatLon?
> >>> If so, what is the changed definition? Providing complete, minimal
> >>> ontologies would help us understand what is wron.
> >>>
> >>> Cheers,
> >>> Evren
> >>>
> >>>> Thanks for your help.
> >>>>
> >>>>
> >>>>
> >>>>
> >>>
> ------------------------------------------------------------------------
> >>>
> >>>> _______________________________________________
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> >>>> http://lists.owldl.com/mailman/listinfo/pellet-users
> >>>> _______________________________________________
> >>>>
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> >>>>
> >>>
> >
> >
>
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