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

>-----Original Message-----
>From: Bijan Parsia [mailto:bparsia@cs.man.ac.uk]
>Sent: Sunday, June 28, 2009 12:47 AM
>To: Michael Schneider
>Cc: Boris Motik; OWL 1.1
>Subject: Re: question on "forest-like anonymous individuals" restriction
>of OWL 2 DL
>
>On 27 Jun 2009, at 17:11, Michael Schneider wrote:
>[snip]
>> But from what you say above, a second issue seems to arise: It looks
>> to me
>> that OWL 2 DL now does not even allow to state /single/ property
>> assertions
>> with blank nodes in both subject and predicate position. Because, as
>> you
>> said, with
>>
>>  ObjectPropertyAssertion( ex:p _:s _:o )
>>
>> one will always also have
>>
>>  ObjectPropertyAssertion( InverseObjectProperty(ex:p) _:o _:s )
>>
>> and so there are in fact always /two/ triples
>
>Triples aren't properties. There's only one property here. One
>relation. Think of the model.
>
>> (though only one of them
>> explicitly stated) with their contained blank nodes building a
>> circular
>> structure.
>
>To have a cycle you need at least two segments. Here you have a line
>which you can go back and forth on.
>
>
>Consider
>	_:x p _:y. _:y p _:z.
>
>You *still* don't have a cycle. You can't get to x, through z without
>going through _:y *twice*. If it were a cycle, you could get back to
>_:x directly.
>
>Cheers,
>Bijan.

I don't think that the "forest-like" restrictions allow to have both
of the above property assertions together in the same ontology. My 
error was to believe that it would already be disallowed to have the 
second /entailed/ by the first. That's /not/ the case. But if I 
explicitly state them both in an ontology 

  ObjectPropertyAssertion( ex:p _:s _:o )
  ObjectPropertyAssertion( InverseObjectProperty(ex:p) _:o _:s )

then there are two distinct property assertions containing 
both _:s and _:o. I understand this to be disallowed in OWL 2 DL,
regardless of what the semantic relationship is between the
property expressions used in the two property assertions.

Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
Research Scientist, Dept. Information Process Engineering (IPE)
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Email: michael.schneider@fzi.de
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