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Re: Top property in property chains for the EL fragment.

From: Rinke Hoekstra <hoekstra@uva.nl>
Date: Wed, 17 Sep 2008 17:44:03 +0200
Cc: "'OWL 2'" <public-owl-wg@w3.org>
Message-Id: <EF288E9A-6CF2-4FB9-B469-19582DA8BCC6@uva.nl>
To: Boris Motik <boris.motik@comlab.ox.ac.uk>

Hi Boris,

On 17 sep 2008, at 17:21, Boris Motik wrote:
> Yes, this is intentional. The goal in the design of all the profiles  
> of OWL 2 was to make them syntactic fragments of OWL 2 DL;
> otherwise, the entire language hierarchy becomes quite messy. As a  
> consequence, the restrictions on not using owl:TopObjectProperty
> in EL++ is "unnecessarily"; however, hardly seems like a reason for  
> concern.

Ok thanks (it got me a bit confused).

Along the same lines, this means that property chains are allowed in  
SubObjectProperty statements, as there are no syntactic restrictions  
that disallows them. Perhaps the 'possibly' should then be removed in  
[3] to make the line less ambiguous.

Best,

	Rinke

>
>
> Regards,
>
> 	Boris
>
>> -----Original Message-----
>> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org 
>> ] On Behalf Of Rinke Hoekstra
>> Sent: 17 September 2008 16:10
>> To: OWL 2
>> Subject: Top property in property chains for the EL fragment.
>>
>>
>> Hi,
>>
>> After reading Uli's response to a question from Jeff Thompson  
>> (below),
>> I just checked the global restrictions section for the EL profile in
>> [1]. It doesn't mention the fact that the top-property is allowed in
>> role chains in the EL fragment (but not in DL itself [2]). Is this
>> intentional?
>>
>> The EL feature overview states "possibly involving property chains"
>> for SubObjectProperty [3]... does this mean we don't know whether
>> property chains can be used in EL? Or that using property chains is
>> allowed?
>>
>> -Rinke
>>
>> [1] http://www.w3.org/2007/OWL/wiki/Profiles#Global_Restrictions
>> [2] http://www.w3.org/2007/OWL/wiki/Syntax#Global_Restrictions_on_Axioms
>> [3] http://www.w3.org/2007/OWL/wiki/Profiles#Feature_Overview
>>
>>
>> Begin forwarded message:
>>
>>> Resent-From: public-owl-dev@w3.org
>>> From: Uli Sattler <sattler@cs.man.ac.uk>
>>> Date: 29 augustus 2008 11:33:31 GMT+02:00
>>> To: Jeff Thompson <jeff@thefirst.org>
>>> Cc: public-owl-dev@w3.org
>>> Subject: Re: owl:TopObjectProperty in property chains?
>>>
>>>
>>>
>>> On 28 Aug 2008, at 08:52, Jeff Thompson wrote:
>>>
>>>>
>>>> Thanks for the references!  These are right on target.  I will
>>>> study them.
>>>> In "Tractable Rules for OWL 2", top of page 6, there is the example
>>>> to translate:
>>>>
>>>> NutAllergic(x) ? NutProduct(y) ? dislikes(x, y)
>>>>
>>>> to
>>>>
>>>> NutAllergic ? ?RNutAllergic.Self
>>>> NutProduct ? ?RNutProduct.Self
>>>> RNutAllergic ? U ? RNutProduct ? dislikes
>>>>
>>>> I'm temporarily gratified that this has the use of the universal  
>>>> role
>>>> in a role chain, similar to my original example (hence the name of
>>>> this
>>>> thread).  But as I study the paper, I suspect it will say that this
>>>> example is not a tractable rule for OWL 2 (despite the title of the
>>>> paper).
>>>>
>>>
>>> Hi Jeff, I didn't mention this example/way of approximating roles in
>>> my previous emails because they require, additionally, some lengthy
>>> explanation about when you can and can't use them without violating
>>> the 'regularity' condition i mentioned......this regularity
>>> condition ensures decidability of reasoning and that our reasoning
>>> techniques work.
>>>
>>> The thing is that, in OWL2  DL, you cannot use owl:TopObjectProperty
>>> in subproperty chains -- you could do so in EL++, a DL described in
>>>
>>> http://www.webont.org/owled/2008dc/papers/owled2008dc_paper_3.pdf
>>>   Pushing the EL Envelope Further. Franz Baader, Sebastian Brandt,
>>> and Carsten Lutz. In Proc. of the Washington DC workshop on OWL:
>>> Experiences and Directions (OWLED08DC), 2008.
>>>
>>> If you want to know more about this, let me know.
>>>
>>> Cheers, Uli
>>>
>>>
>>>> Thanks again,
>>>> - Jeff
>>>>
>>>> Uli Sattler wrote:
>>>>>>>> Notice that the consequent has (x, y), not (x, z) so that z is
>>>>>> unbound.  I think this
>>>>>>>> can done by turning ownsCastle(y, z) into a class description
>>>>>> for y like OwnsCastle(y) with
>>>>>>>> a someValuesFrom restriction on ownsCastle
>>>>>>>>
>>>>>>>> Class: OwnsCastle  SubClassOf: ownsCastle some owl:Thing
>>>>>>>>
>>>>>>>> Then the rule becomes one which can be converted to OWL:
>>>>>>>>
>>>>>>>> hasParent(x, y) ^ OwnsCastle(y) -> hasRichParent(x, y)
>>>>>>>>
>>>>>>>
>>>>>>>> You see what I'm getting at.  In general, I'm interested in
>>>>>> the way that
>>>>>>>> "Rewriting Rules into SROIQ Axioms" turns
>>>>>>>> rules with variables into axioms without variables.
>>>>>>>
>>>>>>> it's described in the papers mentioned earlier...but I think
>>>>>> have a question in mind but you don't want to go through the
>>>>>> algorithm's details?
>>>>>>
>>>>>> I am interested in the algorithm details but fear I don't have
>>>>>> the proper
>>>>>> context for what I was reading.  "Tight Integration of
>>>>>> Description Logics and Disjunctive Datalog"
>>>>>> by Rosati talks about integrating DL database with a Datalog
>>>>>> rules engine
>>>>>> but you are still expected to write the rules in Datalog.
>>>>> aaah, so I can understand your difficulties...you can find a
>>>>> worked-out example that tries to explain the differences between
>>>>> OWL and rules and their interaction in B. Motik, U. Sattler, and
>>>>> R. Studer. Query Answering for OWL-DL with Rules. In  Proc. of the
>>>>> Third International Semantic Web Conference (ISWC 2004), Vol. 3298
>>>>> of Lecture Notes in Computer Science. Springer-Verlag, 2004.
>> http://www.springerlink.com/content/3ah2ypj3p628ft4m/fulltext.pdf
>>>>> ...and you can find out more about translating *some* rules
>>>>> *faithfully* into OWL axioms in E Francis Gasse, Ulrike Sattler,
>>>>> Volker Haarslev: Rewriting Rules into SROIQ Axioms. Description
>>>>> Logics 2008
>>>>> http://ceur-ws.org/Vol-353/GasseSattlerHaarslev.pdf
>>>>> Markus Krötzsch, Sebastian Rudolph, Pascal Hitzler. ELP: Tractable
>>>>> Rules for OWL 2. ISWC2008,  2008.
>> http://korrekt.org/papers/KroetzschRudolphHitzler_ELP_TR_2008.pdf
>>>>> Markus Krötzsch, Sebastian Rudolph, Pascal Hitzler. Description
>>>>> Logic Rules. ECAI2008,  2008. *
>>>>> http://korrekt.org/papers/KroetzschRudolphHitzler_SROIQ-Rules_TR_2008.pdf
>>>>> *
>>>>
>>>>
>>>>
>>>
>>
>> -----------------------------------------------
>> Drs. Rinke Hoekstra
>>
>> Email: hoekstra@uva.nl    Skype:  rinkehoekstra
>> Phone: +31-20-5253499     Fax:   +31-20-5253495
>> Web:   http://www.leibnizcenter.org/users/rinke
>>
>> Leibniz Center for Law,          Faculty of Law
>> University of Amsterdam,            PO Box 1030
>> 1000 BA  Amsterdam,             The Netherlands
>> -----------------------------------------------
>>
>>
>>
>>
>

-----------------------------------------------
Drs. Rinke Hoekstra

Email: hoekstra@uva.nl    Skype:  rinkehoekstra
Phone: +31-20-5253499     Fax:   +31-20-5253495
Web:   http://www.leibnizcenter.org/users/rinke

Leibniz Center for Law,          Faculty of Law
University of Amsterdam,            PO Box 1030
1000 BA  Amsterdam,             The Netherlands
-----------------------------------------------
Received on Wednesday, 17 September 2008 15:44:40 UTC

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