- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Wed, 2 Oct 2002 12:50:46 -0400
- To: webont <www-webont-wg@w3.org>
This one also >Sender: heflin@EECS.Lehigh.EDU >Date: Wed, 02 Oct 2002 12:07:36 -0400 >From: Jeff Heflin <heflin@cse.lehigh.edu> >Organization: Lehigh University >X-Accept-Language: en >To: Jim Hendler <hendler@cs.umd.edu> >Subject: Re: LANG: owl:import - Two Proposals > >Jim, > >Here's another one I think you sent only to me. If you meant to send it >to the mailing list, please do so and I will respond there. > >Jeff > >Jim Hendler wrote: >> >> Elsewhere Jeff asked if those who prefer proposal 1 could address the >> disadvantages of 2 - here's that addressing >> >> > >> > >> >Proposal #2 >> >----------- >> >Syntax: >> >The imports syntax is in the domain of discourse of RDF, but not OWL. >> >Essentially we have a class called owl:Ontology and a property >> >owl:imports which can hold between a pair of Resources. Statements >> >are made about the current document using an empty URI reference >> >(this assumes that this expands to the current URI context). >> >The meaning of any statements which include >> >owl:imports as a subject or object is undefined. Syntactically, this >> >approach is the same as that of DAML+OIL. For example: >> >> >[snip] >> >> > >> >(where merge is as defined in the draft RDF model theory [1]). >> > >> >Pros: >> >- It is possible to query an RDF graph to obtain information about >> >what resources are ontologies and which ontologies import others. >> > >> >Cons: >> >- Having valid syntax that has undefined semantics may lead to reduced >> >interoperability. In particular, some users may build ontologies that >> >rely on the arbitrary decisions made by their favorite tool vendors. >> >> yes - but all langauges have some of these undefined, and we already >> have them in our language unless we go to the strong model Peter >> proposes in which case it is not an OWL document unless a particular >> schema validates it -- As I've said often, my opinion is that that is >> unworkable in the wild. I don't see where there is a problem to say >> it is undefined to doing something that is unlikely to be done >> anyway (i.e. subclassing owl:ontology info or changing it's rdf:type) >> >> but, if some user community finds a reason to do this, implements it, >> and a bunch of people find it useful - then it means the "Owl 2.0" WG >> should look at it -- that's how web languages evolve, and I think it >> is tremendous hubris on the part of our group to think we'll get it >> "right" the first time. >> >> > >> >- It is unclear what it should mean if a document C contains the >> >statement A owl:imports B. Should this be another undefined construct? >> >If so, how can you determine from a graph if the subject of an imports >> >statement is the URI of the document from which the imports statement >> >comes? >> >> I don't understand this. We would have a graph which includes the >> statement in the graph that >> >> :thisDocument owl:importants foo:thatDocument. >> >> this would be useful for people who want to handle name space >> extractions and the like. But rather than arguing this at length, >> let me say that the alternative -- imports not appearing in the graph >> -- certainly provides LESS information than having it. >> >> >- The fact that an ontology's classes and properties do not occur >> >between the <Ontology> tags is unintuitive >> >> I don't disagree with this - but again would ask about instance data. >> I strongly resist having instances HAVE to be in an ontology context >> (because they may be created by tools that are not OWL aware or are >> hand generated - i.e. we create a lot now using the tool "emacs" >> which is a great OWL instance creator (esp. using the DAML mode). >> >> > >> >- The use of about="" to make statements about the enclosing document >> >seems like a hack. In particular is seems like we could be confusing the >> >notion of a document that describes an ontology and the concept of an >> >ontology itself. >> >> I agree, but the problem is the only alternative you offer is to make >> the notion of the document and the ontology be indistinguishable, > > which to me defeats a lot of what I think the SW is all about. I >> would rather see us actually define what an ontology is (see my >> earlier message in the previous thread about having an explicit >> ontology statemtn with a list of the URIs it contains) which would be >> a far more elegant solution to this particular problem which would be >> better than either of the two proposed solutions here -- it didn't >> get enough traction in the WG to be reintroduced here - my point >> being we've already rejected an approach that would solve this >> problem better than proposal 1 does, leading me to believe the WG >> doesn't see this as the critical issue. >> >> >- The approach only partially succeeds in its goals, because although it >> >represents ontologies and their properties, it loses the ability to >> >recognize the boundaries of an ontology (i.e., what it contains) as soon >> >as two or more graphs are merged together. In particular, if this >> >approach is extended for use with versioning, then we lose the ability >> >to know which statements come from which version of an ontology. >> > >> >> I agree, but again if this is what we want critically, we have >> seevral good non-document ways of doing it, which the WG hasn't >> seemed excited by. >> > >> >Recommendation: >> >--------------- >> >Given the pros and cons of each proposal, I have a strong preference for >> >proposal #1, but could live with proposal #2 if the WG was certain that >> >its benefits outweighs its numerous costs. >> >> I'm convinced for 2, not for 1 - so I'd love to see some other >> members of the WG get involved in the discussion... >> >> -- >> Professor James Hendler hendler@cs.umd.edu >> Director, Semantic Web and Agent Technologies 301-405-2696 >> Maryland Information and Network Dynamics Lab. 301-405-6707 (Fax) >> Univ of Maryland, College Park, MD 20742 240-731-3822 (Cell) >> http://www.cs.umd.edu/users/hendler -- Professor James Hendler hendler@cs.umd.edu Director, Semantic Web and Agent Technologies 301-405-2696 Maryland Information and Network Dynamics Lab. 301-405-6707 (Fax) Univ of Maryland, College Park, MD 20742 240-731-3822 (Cell) http://www.cs.umd.edu/users/hendler
Received on Wednesday, 2 October 2002 12:51:38 UTC