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Re: OWL-RL (OWL 2 Profiles)

From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Date: Mon, 8 Dec 2008 10:16:06 +0000
Message-Id: <5CA5343E-82D4-4DF2-8E58-22D4CC5FA3EA@comlab.ox.ac.uk>
Cc: <public-owl-dev@w3.org>
To: Dimitrios Koutsomitropoulos <kotsomit@hpclab.ceid.upatras.gr>

It was decided to integrate these two profiles as follows: An OWL2 RL  
reasoner based on the given rule set can be used to reason with  
arbitrary RDF graphs under the OWL Full semantics. In general, such a  
reasoner will be incomplete, but if the input graph satisfies the  
syntactic part of the profile definition (roughly what was OWL-R DL),  
then the semantics coincide with the direct semantics and the  
reasoner will be complete for atomic query answering (see Theorem PR1  
in Profiles <http://www.w3.org/TR/2008/WD-owl2-profiles-20081202/>).


On 2 Dec 2008, at 15:33, Dimitrios Koutsomitropoulos wrote:

> Could please somebody explain what has happened to OWL-R DL and OWL- 
> R Full?
>> From my understanding, OWL-R DL used to be pure DLP, while OWL-R  
>> Full allows
> all constructs and has no constraints on syntax, but rule-based  
> reasoning
> remains complete only under weaker semantics (I think this profile was
> equivalent to OWLim's OWL Horst). How is this new OWL-RL compared  
> to the
> other two?
> Regards,
> Dimitrios
>> -----Original Message-----
>> From: public-owl-dev-request@w3.org [mailto:public-owl-dev-
>> request@w3.org] On Behalf Of Dimitrios Koutsomitropoulos
>> Sent: Friday, November 07, 2008 10:33 PM
>> To: public-owl-dev@w3.org
>> Subject: RE: Punning between properties types
>> Bijan, thanks for your prompt reply. Please find my
>> comments/understanding
>> below:
>>> -----Original Message-----
>>> From: public-owl-dev-request@w3.org [mailto:public-owl-dev-
>>> request@w3.org] On Behalf Of Bijan Parsia
>>> Sent: Friday, November 07, 2008 9:52 PM
>>> To: Dimitrios Koutsomitropoulos
>>> Cc: public-owl-dev@w3.org
>>> Subject: Re: Punning between properties types
>>> On 7 Nov 2008, at 17:53, Dimitrios Koutsomitropoulos wrote:
>>>> Hello all,
>>>> Regarding the punning issue in OWL 2, I notice than in the new OWL
>>>> 2 semantics document [1], in the changes summary,  punning has been
>>>> disallowed between object and data properties.
>>>> The relevant issue [2] is resolved based on the fact that “there
>>>> are no use-cases” or “we don’t know how to do it”.
>>> No no no! Some people might believe these things but I certainly and
>>> vocally don't ;) There are plenty of use cases and we do know how to
>>> do it. The problem is that in order to disambiguate certain punning
>>> cases in RDF triples we need to introduce new logical vocabulary
>>> (since there is no context for the occurrence of a URI  
>>> node...there's
>>> only one in the whole graph). Some people (most prominently, HP)
>>> objected to this. So, the compromise was to through out all sorts of
>>> punning that in the RDF serialization required new vocabulary.
>>>> From this I understand that an <owl:objectProperty> cannot be
>>>> treated as an <owl:datatypeProperty> and vice-versa.
>>> This is true.
>>>> However what is the deal with <rdf:property> ?
>>> There's no such thing, really, in OWL 2 non-full. Every property is
>>> required to be one or the other (or an annotation propery).
>> So the only legal way for an <rdf:property> to be treated by an OWL 2
>> tool,
>> is to consider the ontology as OWL 2 full. Where I presume this
>> property
>> would be considered *both* as object- and data- and not punned.  
>> But it
>> would
>> still be syntactically correct, whereas in OWL 2 DL it is not  
>> allowed.
>>>> When an rdf ontology is loaded by a reasoner or an application ,
>>>> how should it treat a generic <rdf:property>?
>>> The spec does not say. In the extreme case it could reject the
>>> ontology as malformed (for DL reasoning). Or it could ask the user.
>>> Or it could attempt some repair using heuristics. Or it could  
>>> pass it
>>> on to an OWL Full mode (if there is such).
>> This fullness should imply that no reasoning is to be attempted?
>>>> I see three options:
>>>> -          Such properties should be totally ignored (or should not
>>>> exist all along)
>>>> -          Should be considered only of a fixed type (either data -
>>>> or object-)
>>>> -          Should be punned based on their use
>>> The latter is possible in some cases, but not in every case. A  
>>> simple
>>> example, suppose you have P and C as terms in your ontology and the
>>> declarations:
>>> ObjectProperty(P)
>>> DataProperty(P)
>>> Class(C)
>>> Datatype(C)
>>> Now, what do you do with the expression P some C? Is it an
>>> objectproperty somevalues from or a dataproperty somevaluesfrom, or
>>> both? More to the point what if you want to say that something was P
>>> (object) some C and P (data) all not (datatype) C?
>>> Those parens don't work in RDF.
>>> Now, in many cases we can make good guesses. Tools will have to come
>>> up with them :)
>> Therefore, punning on the types of properties *can* work, at least in
>> some
>> cases, without fullness. For example for those where there are no
>> restrictions on such properties. Shouldn't this part be considered by
>> the
>> OWL 2 spec?
>>>> Latest Protégé 4 (b. 103) seems to follow the last option, with
>>>> which I personally agree. This is also supported by the latest
>> FaCT+
>>>> + (1.2.0)
>>> There is another option: "Determined based on what we can glean of
>>> their use".
>>>> However Pellet 2.0 throws exceptions. Is this a bug or a feature,
>>>> considering the above resolution?
>>> It is conforming. The specs don't say what to do with non-conforming
>>> ontologies. I'd say that one would hope that the tools will do  
>>> better
>>> than throw an exception.
>> Is there a way to guide Pellet to "overcome" such properties? It just
>> seems
>> to consider such properties only as object ones and rejects the
>> ontology
>> when it finds out that they (may) reference data values (I should  
>> have
>> posted this elsewhere but I couldn't help it, sorry)
>>>> In addition, should Protégé 4 and FaCT++ drop this feature?
>> What about Protégé and FaCT++ then? Are they not conforming?
>>>> Finally, is this perhaps an issue different than punning between
>>>> properties (i.e. has nothing to do)?
>>> It's related.
>>  Same with me. Therefore, the WG should look into this. Or at least
>> specify
>> what apps *may* do in such cases.
>> Dimitrios
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Received on Monday, 8 December 2008 10:16:45 UTC

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