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RE: declaredAs

From: Michael Schneider <m_schnei@gmx.de>
Date: Tue, 30 Jan 2007 18:45:34 +0100
Message-ID: <45BF843E.3090500@gmx.de>
To: bmotik@cs.man.ac.uk
CC: public-owl-dev@w3.org, evren@clarkparsia.com, matthew.horridge@cs.man.ac.uk

Hi, Boris!

I did not know about this new feature of "declarations", so I read 
chapter 8 of the current OWL1.1 draft [1]. A few questions arise, both 
from the draft, and from this discussion.

Boris Motik wrote on Fri, 26 Jan 2007:

> There is a big difference between (2) and (3): (3) is used to detect the
> type of P, whereas (2) is used to detect whether P has been explicitly
> declared. Note that (2) implies (3), but not the other way around: 

Does (2), a declaredAs statement, really imply (3), a rdf:type axiom? Or 
is this just a typo?

Say, we have the following ontology:

   :Man rdf:type owl:Class .
   :Woman rdf:type owl:Class .
   :Man owl:disjointWith :Woman .
   :peter rdf:type :Man .

Without any other axioms, this ontology is satisfiable (has a model).

Now, if there is an additional declaration

   :peter owl11:declaredAs :Woman .

and if (2) implies (3), then we can conclude that the additional typing 
statement

   :peter rdf:type :Woman .

holds. Our ontology has become (semantically) inconsistent: The ontology 
is not satisfiable anymore, so every interpretation, which has been a 
model before, isn't a model anymore after adding the declaration.

But the draft says:

   "a declaration is a kind of axiom [...] but it imposes no constraints
   on the model-theoretic interpretation of an ontology"

So, the above semantical change should /not/ have happened by just 
adding a declaration. Is this right?

Thus, I assume it's really meant that (3) implies (2), not the other way 
around. Or did I misunderstand something here?

> Hence, there indeed is a
> need to distinguish the two if you are to completely recover the state of
> the original ontology upon loading.

I can see that declarations and typing axioms are different features: 
Declarations are meant to have no semantical implications at all, while 
typing axioms actually have. But I do not see yet, why declarations are 
really an important feature from a /practical/ point of view.

For instance, section 8.2 of the draft contains the following example:

   Ontology(<http://www.my.domain.com/example>
     SubClassOf( Human Animal )
   )

 From the definition of "structural consistency" (later in the text)

   "An ontology O is structural consistent if each entity occuring
   in an axiom from the axiom closure of O is declared in O".

I can see that the above ontology is /not/ structural consistent: There 
is no declaration for 'Human' and 'Animal'. But when is this a problem?

Please do not consider this question as a trial to flame. :) I probably 
simply do not see a real usecase, because it is the first time I am 
dealing with declarations. But currently I am asking myself, who is 
going to use such declaration statements, instead of simply (ab)using 
rdf:type axioms for this purpose, as it is always done in OWL1.0.

BTW: In the above example, I can at least infer from the subclass-axiom that

   :Human rdf:type owl:Class .
   :Animal rdf:type owl:Class .

So, if (3) really implies (2), as I believe (see above), than we 
actually /have/ declarations for ':Human' and ':Animal'. In this case, 
IMHO another example should be put into the draft.

But please correct me if I am totally miss the point here (quite possible)!


Cheers,
Michael

[1] OWL1.1 draft, "Declarations and Structural Consistency"
     http://owl1-1.cs.manchester.ac.uk/owl_specification.html#8

> 
> Sincerely yours,
> 
> 	Boris
> 
>> -----Original Message-----
>> From: Evren Sirin [mailto:evren@clarkparsia.com]
>> Sent: 26 January 2007 15:22
>> To: Boris Motik
>> Cc: 'Matthew Horridge'; public-owl-dev@w3.org
>> Subject: Re: declaredAs
>> 
>> On 1/26/07 6:27 AM, Boris Motik wrote:
>> > Hello,
>> >
>> > Well, we've been thinking about this, but decided not to do so for an
>> > important reason. Consider an ontology O containing an object property P
>> for
>> > which there is no declaration. A serialization of O into an RDF graph
>> must
>> > ensure the following two things:
>> >
>> > (1) When you parse the graph, you must be able to decode the type of P.
>> > (2) The parsing should correctly restore the "declaredness" status of P
>> --
>> > that is, after parsing, the ontology should not contain a declaration
>> for P.
>> >
>> > Now the problem is that, to ensure compatibility with OWL DL, we use
>> > rdf:type to ensure (1). In the worst case, you really need to include a
>> > triple
>> >
>> > (3) <P, rdf:type, owl:ObjectProperty>
>> >
>> > so that, when you parse the graph, you know what the type of P is. But
>> then,
>> > you should not use rdf:type to reflect the "declaredness" status of P in
>> an
>> > ontology; otherwise, any ontology that contains the triple (3) will also
>> > contain a declaration for P.
>> >
>> Boris, could you explain a little why (2) is needed in the first place.
>> What kind of problems arise if the ontology after parsing contains a
>> declaration for P? If the type of P will be decoded as ObjectProperty in
>> the end, having (3) seems harmless.
>> 
>> Thanks,
>> Evren
>> 
>> > We weren't able to find a way out of this problem and have,
>> consequently,
>> > introduced the owl:declaredAs property.
>> >
>> > Thanks anyway for this suggestion!
>> >
>> > Sincerely yours,
>> >
>> > 	Boris
>> >
>> >
>> >> -----Original Message-----
>> >> From: public-owl-dev-request@w3.org [mailto:public-owl-dev-
>> request@w3.org]
>> >> On Behalf Of Matthew Horridge
>> >> Sent: 26 January 2007 10:06
>> >> To: public-owl-dev@w3.org
>> >> Subject: declaredAs
>> >>
>> >>
>> >> All,
>> >>
>> >> I've been working on an OWL 1.1 parser/renderer recently, and I
>> >> wondered if we could just use rdf:type instead of owl:declaredAs for
>> >> entity declarations in the RDF mapping.  I can't immediately see a
>> >> problem with doing this, and I believe it would improve backwards
>> >> compatibility with the existing "OWL 1.0" RDF/XML mapping.  Any
>> >> thoughts?
>> >>
>> >> Cheers,
>> >>
>> >> Matthew
Received on Tuesday, 30 January 2007 17:46:08 GMT

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