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Re: On the functionalities of the OWL RL profile

From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Date: Mon, 25 Aug 2008 15:02:10 +0100
Message-Id: <BF2D1573-9AA5-4DC1-A6EB-6501D9B08E63@comlab.ox.ac.uk>
Cc: public-owl-wg Group WG <public-owl-wg@w3.org>
To: Ivan Herman <ivan@w3.org>

It's a good point. The original brief when designing the profile/ 
rules was to cover as many features as possible. Clearly, from the  
point of view of the profile design, it would be easy to remove  
reflexivity from the features supported -- the question is whether  
this is a feature that users really want or need. My guess is that  
most users would be willing to sacrifice it, given the potential  
performance hit, but I would like to hear other opinions on that.

A similar question arises w.r.t. the RDF axiomatic triples and  
entailment rules. For example, rules rdfs4a and rdfs4b mean that:

T(?x, ?p, ?y) 	

=>

T(?x, rdf:type rdfs:Resource)
T(?y, rdf:type rdfs:Resource)

Although these triples are relatively harmless, in the sense that  
they typically won't lead to any additional inferences, they do cause  
a significant blow up in the number of triples (up to three times,  
although typically rather less).

Regards,
Ian



On 25 Aug 2008, at 14:23, Ivan Herman wrote:

> Ian,
>
> I changed the subject line because this is not on the unification  
> issue
> and I do not want the tracker to pick it up...
>
> This reflects some discussions we had with Boris but off-list. The
> current OWL RL is relatively large, eg, if one looks at the rule set.
> More to the point, it may add quite a number of extra triples to the
> store (at least conceptually). Maybe it is worth looking at the
> functionalities with a critical eye to see whether it is worth having
> them there (although I am fully aware that this is difficult and a bit
> subjective...).
>
> The specific issue that came up is the possibility of having a  
> reflexive
> property. This leads to the
>
> T(?p, rdf:type, owl:ReflexiveProperty)
> T(?x, ?y, ?z) 	
>
> =>
>
> T(?x, ?p, ?x)
> T(?y, ?p, ?y)
> T(?z, ?p, ?z)
>
> rule, ie, the existence of a single reflexive property would add a  
> huge
> number of triples to the triple set. Although this is technically
> perfectly fine, I was wondering whether it is o.k. to have it there  
> (of
> course, one argument might be that if the user does not want this  
> think
> than, well, (s)he should not use it...). Boris, in a private mail,  
> told
> that reflexive properties are not necessary for OWL RL in general, he
> just copied there in the first draft.
>
> This may be the only example and, if so, we may just want to let it as
> is. But it may be worth looking at the various features with a  
> critical
> eye to see if it is necessary to be there...
>
> Just a thought. Maybe it is worth raising it as a separate issue.
>
> Thanks
>
> Ivan
>
>
> Ian Horrocks wrote:
>>
>> We (Alan and I) agreed that it would help to clarify this issue  
>> and to
>> inform our discussion on Wednesday if the Profiles document [1] were
>> updated to reflect the proposed "unification". This has now been  
>> done.
>> It should be read in conjunction with the (draft) conformance
>> definitions [2].
>>
>> Regards,
>> Ian
>>
>> [1] http://www.w3.org/2007/OWL/wiki/Profiles
>> [2] http://www.w3.org/2007/OWL/wiki/Conformance
>>
>
> -- 
>
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> PGP Key: http://www.ivan-herman.net/pgpkey.html
> FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Monday, 25 August 2008 14:02:47 GMT

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