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Re: OWL DB, OWL UML, etc.

From: Jim Hendler <hendler@cs.umd.edu>
Date: Fri, 14 May 2004 08:44:00 -0400
Message-Id: <p0602044abcca6d100ecd@[192.168.1.26]>
To: Bob MacGregor <macgregor@ISI.EDU>, www-rdf-logic@w3.org
At 23:04 -0700 5/13/04, Bob MacGregor wrote:
Jim,

I reread what you wrote a couple of more times, still find it a bit
confusing, but one phrase that puts me off track is
"how OWL extends the relational calculus".   Properly speaking,
I think you would have to say "how OWL extends a subset
of the relational calculus".   I'm wondering the following:
"Are you giving up some constructs (e.g., compound keys, and the
ability to count) while adding others, or are you imagining adding a
few more OWL constructs to what is already there (yielding a brand
new language strictly more expressive than the relational calculus)?

Cheers, Bob

ok, I guess this could mean a lot of things -- we're looking at the 
fact that some recent papers in the DB community have been discussing 
a notion of ontology as a set of relations and showing how adding 
these relations to the data schema allows improved recall (possibly 
at the cost of precision) for queries against structured DBs.  Simple 
example is what we might call inheritance -- if you say in a typical 
database that clyde is of type "elephant" and query for "animal" you 
won't get Clyde -- with ISA links added in an ontology, then you can 
show this is doable and (with certain extensions) stay within 
polynomial time.  I know that my group proved this in Parka almost a 
decade ago, but database folks don't read AI papers, and the new work 
is actually stronger in that it is more integrated in with the DB 
calculi.   I've been thinking that their results could be extended 
further by using more of OWL's expressivity rather than their purely 
mathematical definitions of what ontological relations are.  Thus, 
OWL DB would be parts of OWL, added to database scheme, which extend 
the recall of database systems by use of OWL modeling constructs (and 
inheriting all the other benefits of OWL - standardization, URI 
based, etc.)   From the DB perspective you wouldn't lose anything - 
keys and etc. would be defined as they currently are - but you would 
gain the ability to use some new expressivity within the rules of the 
game as played by DB, rather than AI, people (i.e. all algorithms 
polynomial, reducible to relational calculus, etc.)  - I guess this 
means I would be thinking of adding some OWL constructs to what is 
already there, thus yielding a new langauge that is more expressive 
than the current relational calculus, without sacrificing the 
expressiveness thereof.
   -JH
p.s. Topic for another time -- seems to be a lot of confusion on this 
list about OWL as a KR langauge and OWL as a standard.  When you say 
"OWL doesn't do xxx" as a KR language you are right -- as a standard, 
all OWL is commited to is having a standard way to write those things 
which we have consensus on how to do.  If you want to use compound 
keys and qualified restrictions, you should add them to the language, 
produce a not explaining how you do so, and explain to people how to 
use them.  If they are indeed useful features, tool vendors will add 
them, people will use them, and they will make it into the next 
version of OWL -- all good web languages evolve over time -- don't 
make the mistake of thinking OWL isn't like that.




At 03:26 PM 5/13/2004, Jim Hendler wrote:

Umm, Bob, I guess I'm confused -- the idea I put forth is to figure 
out how OWL extends the relational calculus --  Let's not confuse 
OWL's ability to model what is in databases (as you discuss) with 
OWL's ability to say things that are not expressible in the database 
schemas themselves (as it is quite an expressive language and can say 
many things way beyond the relation calculus) -- it's not that I 
disagree with what you say above (I don't), it's just that I don't 
see how it relates to what I was asking...
  -JH


--
Professor James Hendler			  http://www.cs.umd.edu/users/hendler
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	  240-277-3388 (Cell)

=====================================
Robert MacGregor
Senior Project Leader
macgregor@isi.edu
Phone: 310/448-8423, Fax:  310/822-6592
Mobile: 310/251-8488

USC Information Sciences Institute
4676 Admiralty Way, Marina del Rey, CA 90292
=====================================


-- 
Professor James Hendler			  http://www.cs.umd.edu/users/hendler 
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	  240-277-3388 (Cell)
Received on Friday, 14 May 2004 08:44:05 UTC

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