Peter F Brown wrote: (01)
> Further, I don't understand why ontology building is an exercise in
> application-specific modelling: I can build an ontology without giving a
> damn about how it's used, where or by who (02)
In so many words, I doubt that.
If you don't know whether, how or why it will be used, why would you bother?
(I realize that like the Red Queen, you didn't say you would, only that you
could. And I can't deny that, even if I try with both hands.) (03)
> - it's my encapsulated take on
> reality and I can then *use* it to build something, if I choose (04)
The problem with a "take on reality" is that a "take" has a viewpoint, which
engenders a degree of accuracy, a scope of interest, a degree of depth, etc.
You can only use an ontology to build something that is consistent with that
viewpoint. (05)
IEEE 1471: Every model has a viewpoint. And an ontology is a model. (06)
> Not so many moons ago, we had an extensive and intensive discussion
> around the differences between data modelling and information modelling
> - and now we have ontology modelling and, why not, concept modelling.
> Would someone venture to distinguish, group, eliminate and add, as
> appropriate? (07)
"What is in a name?" People who distinguish among these ideas have particular
concepts, scopes and (to them) important characteristics in mind. At one time
the term 'data modeling' meant SQL, and was distinguished from 'information
modeling' in that the latter didn't commit directly to a database schema or to
the database concepts 'table and row' versus 'class, property and instance'.
(Among other things, that meant you modeled relationships the same way,
regardless of whether they were 1-to-1, 1-to-many, or many-to-many.) In the
same way right now, some want to use 'data modeling' to mean capturing the
model in XML Schema. (08)
I think it is useful to consider the OMG ideas of the "platform-independent
model" and the "platform-specific model", BUT I think most
"platform-indepedent models" (PIMs) are actually targeted to a specific
implementation technology class in some way. (The original purpose of the OMG
idea was not to throw away everything they learned from CORBA and start over
for J2EE and Webservices. A PIM built from CORBA probably translates quite
well to Java and WSDL/SOAP.) So an 'enterprise object model' PIM that has an
obvious rendering in Java is not likely to have an obvious rendering in SQL. (09)
So, is an information model a PIM? I don't know. But it is some kind of
abstraction from an XML schema or an SQL schema. (010)
Whether a 'data model' means the same thing as 'information model' or means
something like an XML schema is up to the speaker. The ISO 10303 modeling
language EXPRESS says it is a 'data modeling language', and it turns out to be
halfway between the two. "entity" ("class") and "relationship" ("object
property") are not distinguished in the language; so all the "product data
models" in ISO 10303 are thinly disguised SQL models in which "entity" means
'table'. (011)
In a similar way, IMHO, the folks who think their 'ontologies' represent
Platonic truth are deluded. They are models made from a particular viewpoint,
and they are at best accurate from that viewpoint in their time of creation.
Very few truths outside of pure mathematics are timeless. Even accepted
scientific truth undergoes slow refinement. (012)
So I personally would say that an 'ontology' is an 'information model' with
one important distinguishing feature: the language in which the model itself
is captured is well-defined. (NIAM was never formally documented, IDEF1-X had
several fuzzy notions, EXPRESS was badly defined, and UML is deliberately
ambiguous. And so on. ORM may be an exception. Terry Halpin has a formal
logic interpretation for ORM, but it relies on alethic semantics, plus
reification and relational 'projection'.) (013)
That the language is well-defined doesn't make the ontology a better model.
It should make it possible to determine whether a given ontology really is
"correct" or "complete" in some particular viewpoint. And on a few occasions,
it may make it possible to know when two concepts really are the same, in
spite of different authors, different viewpoints in construction, and
different terminology. (And no information model was sufficient for that.) (014)
-Ed (015)
--
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 (016)
"The opinions expressed above do not reflect consensus of NIST,
and have not been reviewed by any Government authority." (017)
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