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Re: OWL reasoning in rules

From: Ulrike Sattler <sattler@cs.man.ac.uk>
Date: Fri, 25 May 2007 11:26:34 +0100
Message-Id: <3AC5B858-5F91-4CB8-B27F-55A1F4DE3D4B@cs.man.ac.uk>
Cc: Matt Williams <matthew.williams@cancer.org.uk>, Owl Dev <public-owl-dev@w3.org>, Semantic Web <semantic-web@w3.org>
To: Ian Horrocks <horrocks@cs.man.ac.uk>

Hi Matt, let me add a reference to a paper that contains an  
explanation of why combining two decidable formalisms, OWL and rules,  
might lead to an undeciable one, and which explains the differences:

Boris Motik, Ulrike Sattler, and Rudi Studer. Query Answering for OWL- 
DL with rules. Journal of Web Semantics: Science, Services and Agents  
on the World Wide Web, 3(1):4160, 2005.
http://www.cs.man.ac.uk/~bmotik/publications/papers/mss05query- 
journal.pdf

Cheers, Uli

On 25 May 2007, at 11:02, Ian Horrocks wrote:

>
> Hi Matt,
>
> It isn't completely clear whether you are asking about using some  
> kind of rule engine to reason with OWL or extending OWL with rules;  
> I will assume that it is the former.
>
> It is pretty easy to write some sound inference rules for OWL; what  
> is difficult is guaranteeing completeness and termination. This is  
> made more tricky by that fact that the semantics of rule systems  
> generally assume a closed domain (the only individuals that exist  
> are those that are explicitly mentioned in the ontology), whereas  
> the semantics of OWL allows for the existence of (a possibly  
> infinite number of) additional unnamed individuals -- in fact there  
> exist OWL ontologies for which all models have domains of infinite  
> size.
>
> Incompleteness may be a much more serious problem that it at first  
> appears, because failure to derive a positive result is invariably  
> interpreted as a negative result -- which is obviously incorrect in  
> general. There may be applications where this incorrectness is not  
> much of an issue, but there are also many where it is -- see [1]  
> for an example where incomplete reasoning could have led to  
> patients being mis-diagnosed. Moreover, given that several highly  
> efficient and correct reasoners are available, one would presumably  
> need a pretty compelling reason to want to develop/use an incorrect  
> one.
>
> There are lots of papers on reasoning with OWL that you can read in  
> order to get an idea of what is needed in order to guarantee  
> correctness: [2] describes a tableau based method, and [3]  
> describes a method based on a (highly non-trivial) reduction to  
> disjunctive datalog rules.
>
> Regards,
>
> Ian
>
> [1] http://owl-workshop.man.ac.uk/acceptedPosition/submission_19.pdf
> [2] http://www.cs.man.ac.uk/~horrocks/Publications/download/2007/ 
> HoSa07a.pdf
> [3] http://www.cs.man.ac.uk/~bmotik/publications/papers/hms07query- 
> journal.pdf
>
>
> On 25 May 2007, at 09:54, Matt Williams wrote:
>
>>
>> Dear All,
>>
>> I was wondering if anyone can give me some precise pointers as  to  
>> why implementing OWL reasoning on rules is so hard?
>>
>> There seem to be lots of systems that do subsets of OWL as rules,  
>> but I'm still unclear about what features in OWL don't work when  
>> translated into rules.
>>
>> Thanks a lot,
>>
>> Matt
>> -- 
>> http://acl.icnet.uk/~mw
>> http://adhominem.blogsome.com/
>> +44 (0)7834 899570
>>
>
>

Ulrike Sattler
sattler@cs.man.ac.uk
http://www.cs.man.ac.uk/~sattler/
Received on Friday, 25 May 2007 10:31:44 GMT

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