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[protege-owl] Query about constructing an ontology based on received OWL-DL fragments on your behalf

Thomas Schneider tschneider at informatik.uni-bremen.de
Fri Feb 10 13:27:53 PST 2012


On 10.02.2012, at 20:50, Timothy Redmond wrote:

> On 2/8/12 1:51 AM, William Fitzgerald wrote:
>> Hi Thomas
>> 
>>> Timothy's description is an excellent pointer to locality-based modules which are currently supported by the OWL API, but not yet by a Protégé plugin. The most convenient way to extract them is probably via the web service:
>>> 
>>> http://owl.cs.manchester.ac.uk/modularity/
>> 
>> Excellent resource.
>> 
>> Perhaps this is a silly question/comment (and while not a research area of my own) but I presume its not trivial to extract the minimum set of axioms, classes, individuals and property relations required to describe a given module. What I mean is, it may not be easy to know when to stop adding knowledge about a particular concept or individual for example within a module without ending up adding the entire ontology.
> 
> Not trivial but the description logic experts have found a relatively simple approach that generates modules for OWL files.
> 
> There are two issues.  First you said "minimum".  Even for OWL getting the absolute minimal module is difficult (I forget how difficult but there are references that talk about this).  

For OWL: undecidable. For DLs below OWL, including the EL profile: usually at least by an exponential harder than plain reasoning tasks such as satisfiability. This holds for the problem "given an ontology O and a set S of entities, return the minimal subset of O which entails all statements formulated in S that follow from O". If you want a close-to-minimal subset with this guarantee, you can use locality-based modules. They are extracted using a purely syntactic condition to be checked for single axioms of the ontology.

There's some explanation of locality-based modules at http://owl.cs.manchester.ac.uk/research/topics/modularity/ -- with references for further reading, but I just noticed that those are missing. I'll contact the maintainers of the page.

> The solution found by the description logic community is to find a module that may not be minimal but which can be found efficiently and is useful in practice.
> 
> Secondly, the fact that these modules can be found at all is an interesting fact about the OWL language.  In other more expressive languages, the module notion can still be defined but finding modules is probably very difficult to impossible.

Actually, locality can straightforwardly be extended to first-order logic. The problem is whether the approximation is still good enough -- without further investigation, there's some evidence that the syntactic locality test is too insensitive, which leads to many more axioms than necessary being included in a module.

Cheers

Thomas

> 
> -Timothy
> 
> 
>> 
>> I am looking forward to exploring OWL-2 via Protege 4 and OWL-Java API. What had previously stopped me was the use of SWRL and SQWRL that I applied to my own area of security research.
>> 
>> Many thanks,
>> Will.
>> 
> 
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----------------------------------------------------------------------
Dr. Thomas Schneider
Universität Bremen, FB 03
MZH, Raum 3100
Postfach 330440
28334 Bremen
Germany
+49 421 218-64432
http://www.informatik.uni-bremen.de/~ts/
----------------------------------------------------------------------

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