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Re: [ontolog-forum] Ontology-based database integration

To: "Burkett, William [USA]" <burkett_william@xxxxxxx>
Cc: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Edward Barkmeyer <edward.barkmeyer@xxxxxxxx>
Date: Wed, 07 Oct 2009 15:07:56 -0400
Message-id: <4ACCE70C.5050505@xxxxxxxx>
Bill Burkett wrote:
> Something that you don't mention, however, is that the value often touted for 
>ontologies and the use OWL is that because it's logic based you can do 
>reasoning/inferencing with OWL representations and discover "new" information. 
> Unfortunately, to get the semantic expressiveness that you see in semantic 
>data modeling languages, you need to use OWL-Full - and there is no guarantee 
>that you successfully reason/inference over OWL-Full representations (or at 
>least bring that reasoning/inferencing to completion over a finite amount of 
>       (01)

This is true of _some_ of the expressive capabilities of SDM languages.  
If you are thinking of EXPRESS and OCL as "semantic data modeling" 
languages, then yes, you can write very complex integrity rules in those 
languages.  But EXPRESS, for example, forces the use of complex 
expressions to express a number of simple relationships for which OWL 
has explicit syntax.  And OWL can directly capture all of the common 
semantic relationships (as distinct from all kinds of integrity 
constraints).    (02)

> Thus, the main value of OWL is compromised and it becomes essentially 
>equivalent to other semantic data modeling languages.
> Am I missing something, or are the other values that can be derived from an 
>OWL representation if you set aside the advantage of being able to 
>successfully reason over the it?
>       (03)

The main advantage is that the semantics of the OWL constructs 
themselves is formally defined.  We know exactly what a particular OWL 
expression means; we don't have to talk about modeling styles and the 
conventions used by group X.  This is a major difference from UML and 
EXPRESS and IDEF1-X, in which one can never be certain whether a given 
model element represents a concept or a data structure.  Both NIAM/ORM 
and SDM had formal semantic models defined for them "after the fact", 
which unfortunately doesn't mean that models made in those languages had 
exactly those interpretations.  In the case of OWL, that formal 
semantics is part of the definition of the language -- if you use an OWL 
construct with another intent, your model does not mean what you think 
it means.    (04)

Now, I think that "setting aside the ability to reason" is rather like 
ordering "a hamburger -- hold the beef".  For the kind of thing Len is 
doing, for example, you don't need OWL/Full in most cases.  Much of that 
semantic analysis is about classification and the relationships between 
classifications of things and data structures representing the things.  
NIST and other experiments in "semantic mediation" indicate that OWL/DL 
(and "extended tableaux reasoning") is fairly powerful in this regard.  
In most cases, perhaps 5% of the knowledge content associated with data 
schemas cannot be captured in OWL/DL.  But the impact of that 5% on 
conversions or analysis is much harder to judge.  So if Bill needs 100% 
knowledge transfer, then OWL/DL and tableaux reasoning will fail his 
test; but if you are trying to get useful practical results, OWL/DL can 
go a long way.    (05)

(Now, since I know Bill from the ISO TC184 EXPRESS data modeling 
activities of the last 20 years, I realize that many of his "semantic 
data models" are probably EXPRESS models with ornate rulesets.  Many of 
those are built around geometry, which one would never want to do in 
OWL.  So I freely admit that OWL/DL won't go a long way in capturing those.)    (06)

> P.S. I'd be very interested in seeing the presentation you mention - is it 
>something you can distribute? (at least to me?  :-)
>       (07)

FWIW, I did the presentation on one of the Ontology Forum Webinars in 
2007, and the slide set (and the recording, Peter being so well 
organized) is on the wiki at:
http://ontolog.cim3.net/cgi-bin/wiki.pl?ConferenceCall_2007_04_12    (08)

-Ed    (09)

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    (010)

"The opinions expressed above do not reflect consensus of NIST, 
 and have not been reviewed by any Government authority."    (011)

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