RE: question on "forest-like anonymous individuals" restriction of OWL 2 DL

Hi Ian!

Yes, I got confused: The restrictions do not take inferred statements into
account.

Also, from what you say below I now see that even "diamond-shaped"
structures are disallowed in OWL 2 DL, e.g.

  _:x ex:p _:y .
  _:x ex:q _:y .

And since only syntax counts, it wouldn't even help to have another axiom
stating

  ex:p owl:equivalentClass ex:q .

right?

Cheers,
Michael

>-----Original Message-----
>From: Ian Horrocks [mailto:ian.horrocks@comlab.ox.ac.uk]
>Sent: Sunday, June 28, 2009 12:12 AM
>To: Michael Schneider
>Cc: OWL 1.1; Boris Motik
>Subject: Re: question on "forest-like anonymous individuals" restriction
>of OWL 2 DL
>
>I think that the confusion arises from the fact that the forest in
>question is not defined by the ontology assertions. The point is that
>in order for the ontology to be in OWL 2 DL it must be possible to
>arrange the anonymous individuals in a forest such that the three
>conditions (which *do* refer to ontology assertions) are satisfied.
>In the case of the second example, it is easy to see that there can
>be no such forest satisfying both the first and second conditions,
>namely:
>
>"for each assertion in Ax of the form ObjectPropertyAssertion( OPE
>_:x _:y ), either _:x is a child of _:y or _:y is a child of _:x in F"
>
>and
>
>"for each pair of anonymous individuals _:x and _:y such that _:y is
>a child of _:x in F, the set Ax contains at most one assertion of the
>form ObjectPropertyAssertion( OPE _:x _:y ) or ObjectPropertyAssertion
>( OPE _:y _:x )".
>
>In fact the purpose of adding the second example was to emphasise
>that not only cycles, but any non-tree like arrangement of anonymous
>individuals is illegal in OWL 2 DL.
>
>Regards,
>Ian
>
>
>On 27 Jun 2009, at 01:01, Boris Motik wrote:
>
>> Hello,
>>
>> No, not really: since OWL 2 has inverse roles, the actual
>> directionality of the
>> property assertions doesn't matter. That is, the role assertion
>>
>> ObjectPropertyAssertion( a:hasDaughter _:b1 _:b2 )
>>
>> is equivalent to
>>
>> ObjectPropertyAssertion( InverseObjectProperty(a:hasDaughter) _:b2
>> _:b1 )
>>
>> Now if the latter is circular, the former should be circular as
>> well, given that
>> the two assertions are semantically equivalent.
>>
>> Regards,
>>
>> 	Boris
>>
>>> -----Original Message-----
>>> From: Michael Schneider [mailto:schneid@fzi.de]
>>> Sent: 27 June 2009 01:52
>>> To: Boris Motik
>>> Cc: OWL 1.1
>>> Subject: RE: question on "forest-like anonymous individuals"
>>> restriction of
>>> OWL 2 DL
>>>
>>> Hi Boris!
>>>
>>> The second counter example states
>>>
>>>   ObjectPropertyAssertion( a:hasChild _:b1 _:b2 )
>>>   ObjectPropertyAssertion( a:hasDaughter _:b1 _:b2 )
>>>
>>> But shouldn't it be
>>>
>>>   ObjectPropertyAssertion( a:hasChild _:b1 _:b2 )
>>>   ObjectPropertyAssertion( a:hasDaughter _:b2 _:b1 )
>>>                                          ^^^^^^^^^
>>>
>>> in order to build a circular structure?
>>>
>>> Cheers,
>>> Michael
>>>
>>>> -----Original Message-----
>>>> From: Boris Motik [mailto:boris.motik@comlab.ox.ac.uk]
>>>> Sent: Friday, June 26, 2009 1:29 PM
>>>> To: Michael Schneider; 'OWL 1.1'
>>>> Subject: RE: question on "forest-like anonymous individuals"
>>>> restriction
>>>> of OWL 2 DL
>>>>
>>>> Hello,
>>>>
>>>> In response to Michael's comment, Ian and I have made the following
>>>> changes to
>>>> the Syntax document:
>>>>
>>>> http://www.w3.org/2007/OWL/wiki/index.php?
>>>> title=Syntax&diff=24654&oldid=
>>>> 24647
>>>>
>>>> I hope things are clearer now. Please let me know should you have
>>>> any
>>>> comments.
>>>>
>>>> Regards,
>>>>
>>>> 	Boris
>>>>
>>>>> -----Original Message-----
>>>>> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-
>>>> request@w3.org] On
>>>>> Behalf Of Michael Schneider
>>>>> Sent: 29 May 2009 20:46
>>>>> To: OWL 1.1
>>>>> Subject: question on "forest-like anonymous individuals"
>>>>> restriction
>>>> of OWL 2
>>>>> DL
>>>>>
>>>>> Hi all!
>>>>>
>>>>> I had to explain to someone the "forest-like anonymous individuals"
>>>>> restriction of OWL 2 DL (Section 11.2 of the Structural Spec),
>>>>> but I
>>>> found
>>>>> myself uncertain about it. In particular, I'm unclear how
>>>>> "fixed" the
>>>> variable
>>>>> "OPE" is in the set of conditions.
>>>>>
>>>>> But it's easier to show my problem by an example: It's clear to me
>>>> (also from
>>>>> the example following the formal definition) that the following is
>>>> /not/
>>>>> allowed in OWL 2 DL:
>>>>>
>>>>>   _:x :p _:y
>>>>>   _:y :p _:x
>>>>>
>>>>> But what about
>>>>>
>>>>>   _:x :p _:y
>>>>>   _:y :q _:x
>>>>>
>>>>> with /different/ properties?
>>>>>
>>>>> Michael
>>>>>
>>>>> --
>>>>> Dipl.-Inform. Michael Schneider
>>>>> Research Scientist, Dept. Information Process Engineering (IPE)
>>>>> Tel  : +49-721-9654-726
>>>>> Fax  : +49-721-9654-727
>>>>> Email: michael.schneider@fzi.de
>>>>> WWW  : http://www.fzi.de/michael.schneider
>>>>>
>>>> ====================================================================
>>>> ===
>>>>> FZI Forschungszentrum Informatik an der Universität Karlsruhe
>>>>> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
>>>>> Tel.: +49-721-9654-0, Fax: +49-721-9654-959
>>>>> Stiftung des bürgerlichen Rechts, Az 14-0563.1, RP Karlsruhe
>>>>> Vorstand: Prof. Dr.-Ing. Rüdiger Dillmann, Dipl. Wi.-Ing. Michael
>>>> Flor,
>>>>> Prof. Dr. Dr. h.c. Wolffried Stucky, Prof. Dr. Rudi Studer
>>>>> Vorsitzender des Kuratoriums: Ministerialdirigent Günther
>>>>> Leßnerkraus
>>>>>
>>>> ====================================================================
>>>> ===
>>>>>
>>>>
>>>
>>> --
>>> Dipl.-Inform. Michael Schneider
>>> Research Scientist, Dept. Information Process Engineering (IPE)
>>> Tel  : +49-721-9654-726
>>> Fax  : +49-721-9654-727
>>> Email: michael.schneider@fzi.de
>>> WWW  : http://www.fzi.de/michael.schneider
>>> =====================================================================
>>> ==
>>> FZI Forschungszentrum Informatik an der Universität Karlsruhe
>>> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
>>> Tel.: +49-721-9654-0, Fax: +49-721-9654-959
>>> Stiftung des bürgerlichen Rechts, Az 14-0563.1, RP Karlsruhe
>>> Vorstand: Prof. Dr.-Ing. Rüdiger Dillmann, Dipl. Wi.-Ing. Michael
>>> Flor,
>>> Prof. Dr. Dr. h.c. Wolffried Stucky, Prof. Dr. Rudi Studer
>>> Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
>>> =====================================================================
>>> ==
>>
>>
>>