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Re: A slight issue with datatypes in OWL 2 RL

From: Ivan Herman <ivan@w3.org>
Date: Fri, 23 Jan 2009 11:42:39 +0100
Message-ID: <49799F1F.7050509@w3.org>
To: Boris Motik <boris.motik@comlab.ox.ac.uk>
CC: 'W3C OWL Working Group' <public-owl-wg@w3.org>
Each new datatype has to be implemented somehow (interpretation of the
lexical space rules, relationships to other, etc, etc). The
implementation of any of those can be non-trivial. So we are just adding
new and new non-trivial things.

Ivan

Boris Motik wrote:
> Hello,
> 
> I agree that the implementation of datatypes is nontrivial in OWL 2 RL. This, however, is already the case for the existing
> datatypes. I really cannot see how the datatypes that we left out would make the implementation any harder.
> 
> Regards,
> 
> 	Boris
> 
>> -----Original Message-----
>> From: Ivan Herman [mailto:ivan@w3.org]
>> Sent: 23 January 2009 08:51
>> To: Boris Motik
>> Cc: 'W3C OWL Working Group'
>> Subject: Re: A slight issue with datatypes in OWL 2 RL
>>
>> Boris,
>>
>> before we do this... let me just raise this issue: just because we _can_
>> does not meant that we necessarily _should_.
>>
>> In my view, one of the goals of RL is a possibility for an easy
>> implementation, too. With my limited implementation experience the
>> datatype handling of RL is by far the most complex part of an
>> implementation. Sure, if one goes for a very efficient implementation
>> then taking care of things like owl:sameAs becomes also more complex,
>> but that is not 100% necessary for a compliant thing. Datatype handling
>> is. (I actually did not even have the time to implement it, I just rely
>> on the underlying RDF/Python environment and do whatever it can do. I
>> can see many implementations doing just that.) Oracle has already
>> indicated that they are not really in favour of an owl:rational
>> inclusion in OWL RL, and I think their reaction reflects the same concerns.
>>
>> Based on this I actually do _not_ believe that this is just an editorial
>>  comment but would definitely warrant a new LC round because it would
>> significantly add to the complexity of implementations. My personal
>> interpretation (maybe wrong!) of that comment in the document is that
>> some datatypes (like rational) may actually be dropped from the list and
>> not add all other datatypes blindly...
>>
>> My 2 cents...:-)
>>
>> Ivan
>>
>> Boris Motik wrote:
>>> Hello,
>>>
>>> Here is a Last Call comment about datatypes in OWL 2 RL. This issue was pointed out by Jos de
>> Bruijn during the RIF integration
>>> meeting, and I remembered it today after a private discussion about datatypes with Zhe. Thanks to
>> both of them!
>>> Currently, OWL 2 RL disallows certain datatypes on the grounds that reasoning with them would not
>> be polynomial. Now we could
>>> actually relax this restriction and allow all OWL 2 datatypes to occur in OWL 2 RL ontologies.
>>>
>>> This is actually an oversight of mine, caused by the following technical issue. OWL 2 EL and OWL 2
>> QL have existential quantifiers;
>>> hence, you can state existence of concrete objects whose values is not known precisely. But then,
>> if you allow combinations of
>>> datatypes such that the intersection of possibly negated datatypes is finite, you really do get
>> into problems: your reasoning
>>> suddenly becomes NP-hard because you need to start guessing the appropriate value of existentially
>> implied object. To prevent this
>>> from occurring, I selected the set of allowed datatypes in OWL 2 EL such that each intersection of
>> possibly negated datatypes is
>>> either empty or infinite; then, I merely copied this set to all the profiles.
>>>
>>> As Jos rightly pointed out at the RIF integration meeting, however, OWL 2 RL *does not* have
>> existential quantifiers; consequently,
>>> the value of each concrete object is fully known. But then, there is no need to actually restrict
>> the set of datatypes: to support a
>>> datatype, you just need a procedure that recognizes whether some literal is in the range of a
>> particular datatype (which is easy to
>>> do for all of OWL 2 datatypes).
>>>
>>>
>>> The fix to this comment would be to revise the datatypes section for OWL 2 RL and allow all OWL 2
>> datatypes to occur in OWL 2 RL
>>> ontologies. Since we already have a note saying that the set of supported datatypes might change, I
>> believe that this change would
>>> not warrant another Last Call round.
>>>
>>> I'm really sorry about this oversight!
>>>
>>> Regards,
>>>
>>> 	Boris
>>>
>>>
>> --
>>
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> mobile: +31-641044153
>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>> FOAF: http://www.ivan-herman.net/foaf.rdf
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf


Received on Friday, 23 January 2009 10:43:12 GMT

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