Ed, (01)
"I come to bury Caesar, not to praise him" (02)
The title for this thread is "interpreting OWL"; the discussion of
EXPRESS was a thought experiment to see just how perversely one could
interpret OWL, essentially as a way of asking, "What level of
interoperability does one get from using OWL?" The answer has come back,
loud and clear, "OWL doesn't help at all." This is not a discussion I'd
observed before, but is important in setting the right (low) level of
expectation for the Semantic Web. (03)
------------- (04)
Following the comments about not being able to represent cyclic
structures in OWL, my hacker's instincts kicked in, and remembering that
EXPRESS data models can be translated into XML messages, which are also
tree structured, it strikes me that one could: (05)
a) Define two integer properties Id, and Ref
b) Create an implied relationship, that a value of Ref is a link to a
thing with its Id the same value as Ref
c)
Id Ref
1 2
2 3
3 1 (06)
While this is not a mechanism explicitly understood by OWL, it a cyclic
structure that could be expressed in OWL. (07)
Given lots of cunning graduates being expected to provide theses using
OWL, one can confidently predict that where it does not do what they
want directly, it will be twisted to do it indirectly.
As Matthew said: (08)
"MW: Without something that was effectively an upper ontology (and
people agreeing to use the one way of implementing it in OWL - or
whatever) then you have little chance of integrating anything except
with a pot puri of interfaces." (09)
> -----Original Message-----
> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
> [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ed
> Barkmeyer
> Sent: 18 October 2010 18:23
> To: ian@xxxxxxxxxxxxxxxx; [ontolog-forum]
> Subject: Re: [ontolog-forum] Interpreting OWL
>
>
> *** WARNING ***
>
> This message has originated outside your organisation,
> either from an external partner or the Global Internet.
> Keep this in mind if you answer this message.
>
>
> Ian,
>
> I tend to agree with your comments. Notes embedded.
>
> Ian Bailey wrote:
>>
>> Hi Sean,
>>
>>
>>
>> I would be tempted to leave OWL out of the equation altogether for
>> EXPRESS, and use RDF/RDFS. The most used OWL representation is the RDF
>
>> one, so I think this makes sense for EXPRESS too.
>>
>
> This is also what David Price suggested. The question that has not been
> answered is: Why OWL? What is it that Sean and gang want to get from
> OWL, other than academic acceptance of their work (John Sowa's codicil
> being relevant in that regard)?
>
>> I think you could do a pretty good job of modelling the EXPRESS
>> meta-model in RDF(S). It would avoid a lot of the baggage that comes
>> with OWL (I can hear the DL nuts lighting their torches as I type) and
>
>> would be using a similar approach to the RDF form of OWL. This would
>> then make the comparison you mention a bit more straightforward.
>>
>
> I pointed to the EXPRESS MM specification in my previous email. OMG is
> currently near standardization of an RDF(S) form of the MOF, which gives
> the metamodel a standard RDF form (for what that may be worth).
>
>> There are a few oddball aspects in EXPRESS such as SELECTs and
>> SUPERTYPE OF clauses that, although they'll map, won't turn out quite
>> as the STEP community would expect them to.
>>
>
> Interesting. I think SUPERTYPE (and SUBTYPE_CONSTRAINT its preferred
> EXPRESSv2 form) should map very readily to useful OWL constructs. The
> one thing DLs do well is describing relationships among Sets. If that
> isn't what the STEP community expects, they don't know what their model
> means.
>
> Similarly, a SELECT type is just an after-the-fact supertype, typically
> created in order to define the domain or range of some property or
> properties. This is also something that is easy to do in OWL/DL, with
> exactly the EXPRESS interpretation. What OWL doesn't have is the
> EXPRESS computational overload in the assumption that an instance can be
> asked what all types it instantiates. That is a purely programming
> language idea. Logically it makes no sense at all. It IS meaningful to
> ask whether a given thing is an instance of a given type -- it is
> something you ask all the time in SPARQL. (I lost this modeling battle
>
> with the EXPRESS Committee in SC4/WG5 in 1989, thus creating 20 years of
> bad modeling practice.)
>
>> All you need to do then is persuade the OMG to do the same thing -
>> though there is the added complication of UML being wedded to MOF.
>>
>
> I missed some connection here. I think what Ian is saying is that there
> should be a standard RDF form of the OMG EXPRESS metamodel. See above.
>
> The limitations of MOF have had only minor consequences for the EXPRESS
> Metamodel. Bear in mind that the metamodel defines, for example,
> SelectType as a meta-class of things that may appear in an EXPRESS
> schema. It does not attempt to assign any UML meaning to those things;
> it assigns the SelectType (EXPRESS SELECT) meaning to those things. We
> modeled the EXPRESS language. Mapping the concepts of that metamodel to
> concepts of the UML metamodel or concepts of the OWL metamodel is a
> separate task. All the EXPRESS Metamodel provides is the formal
> meta-objects that such a mapping can manipulate. Where there are no
> exact equivalents, the mapped image of an EXPRESS model element will
> suffer from losses of some semantics in the domain element and/or gains
> of unintended semantics in the range element.
>
>> An RDFS representation of MOF might even give us a replacement for XMI
>
>> that actually works, and that can't be a bad thing.
>>
>
> That is one of the motivations of the MOF2RDF proposers, although it is
> impolitic to state it formally in an OMG RFP. The real argument is that
> XMI is a foreign language to almost all programmers, whereas RDF has a
> significant presence in the larger "modeling community" that includes
> XMI's only constituency.
>
> With respect to XMI, OMG finally decided that its reputation was at
> stake and "locked the UML vendors in a room" -- the Model Interchange
> Committee -- to agree on a standard interpretation of UMLv2 into an
> interchange form. We are finally, after only 5 years, beginning to see
> XMI interchange work among UML tools.
>
> -Ed
>>
>>
>>
>> Cheers
>>
>> --
>>
>> Ian
>>
>>
>>
>> *From:* ontolog-forum-bounces@xxxxxxxxxxxxxxxx
>> [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] *On Behalf Of *sean
> barker
>> *Sent:* 17 October 2010 12:17
>> *To:* ontolog-forum@xxxxxxxxxxxxxxxx
>> *Subject:* [ontolog-forum] Interpreting OWL
>>
>>
>>
>>
>>
>> Apologies for asking another question before I have finished
>> responding to the last, but a question arose at the last STEP meeting
>> which has some tricky implications.
>>
>>
>>
>> The statement was made that anything that could be written in EXPRESS
>> could be written in OWL. However, some of the constructs in EXPRESS,
>> particularly those concerning the cardinality and structure of
>> relationships are not directly obviously expressible in OWL, such as
>> the distinction between a bag and a set. However, it should be
>> possible to create a first order interpretation of OWL such that an
>> EXPRESS relationship is a subtype of 'thing', and the relationship
>> constraints are then OWL properties. EXPRESS Entity and Type also
>> become subtypes of 'thing'
>>
>>
>>
>> This then allows one to construct a second order interpretation by
>> suptyping Entity, Relationship and Type as STEP generic entities, such
>
>> as Product, Version, View, Property, Property-Representation,
>> Representation-Presentation etc. That is, EXPRESS entities provide an
>> upper level ontology for STEP in OWL.
>>
>>
>>
>> One can then create a third order interpretation, as is done in the
>> STEP Application Protocols, in which the STEP generic entities are
>> interpreted in the context of a business process, so that Product is
>> either a product (AP 203) a part (AP 214) or a technical data package
>> (AP 232).
>>
>>
>>
>> Two questions arise. Firstly, one could also describe other modelling
>> languages such as UML and IDEF1X as first order interpretations of OWL
>
>> (in the sense above) (and even of OWL itself). Could one then compare
>> the expressive power of such formalisation by creating a lattice of
>> modelling languages? (This would also expose ambiguities in the
>> languages).
>>
>>
>>
>> Secondly, would the second and third order interpretations be
>> compatible with anybody else's use of OWL? For example, whether a
>> particular (EXPRESS) property is a property of a product is contingent
>
>> on the Version (an implied temporal commitment) and the View.
>>
>
> --
> Edward J. Barkmeyer Email: edbark@xxxxxxxx
> National Institute of Standards & Technology
> Manufacturing Systems Integration Division
> 100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
> Gaithersburg, MD 20899-8263 FAX: +1 301-975-4694
>
> "The opinions expressed above do not reflect consensus of NIST,
> and have not been reviewed by any Government authority."
> (010)
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