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Re: semantics of daml:equivalentTo [was: Comments on Annotated DAML 1.6]

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 13 Oct 2000 12:00:45 -0500
Message-Id: <v04210103b60ce6cf19a2@[]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: www-rdf-logic@w3.org
>From: Jeff Heflin <heflin@cs.umd.edu>
>Subject: Re: semantics of daml:equivalentTo [was: Comments on 
>Annotated  DAML   1.6]
>Date: Thu, 12 Oct 2000 15:29:56 -0400
> > I'd just like to elaborate on Jim's message. I believe that equivalentTo
> > is the DAML version of the SHOE <DEF-RENAME> element. In SHOE,
> > DEF-RENAME allows an ontology to provide an alias for a term defined
> > elsewhere. Essentially, it means that both terms reference the same
> > concept, and thus any assertion that is made using one term is also true
> > if the other term was substituted in its place. This is really easy to
> > implement: you keep a hash table that matches aliases with the base
> > terms (used in the original definitions) that they renamed, and upon
> > parsing a document or issuing a query you can perform the necessary
> > substitutions to rephrase it in only base terms.
> >
> > Because of the confusion that equivalentTo has caused on this list,
> > perhaps "renames" or "aliasOf" are better choices for the propery name?
> >
> > Jeff
>OK, here is where I feel that I must put in a scream for formality, or at
>least clarity. What does it matter whether the name is equivalentTo, 
>renames, aliasOf, or frobaz?  What matters, as far as I can see, is 
>what the meaning of
>"equivalentTo" is.

Well said. I agree with Peter here that we have to have some account 
of meaning which goes a little higher than implementation.  There is 
a reasonably well-defined meaning for equality (=identity = 
equivalence) which is pretty much what Jeff says above: it means that 
the terms refer to the same thing. So to assert
  equivalentTo(X, Y)
is to claim that X and Y have the same denotation. Now, this in turn 
is just as clear or as murky as the notion of denotation is for X and 
Y. Maybe it would help, therefore, if we could have a sketch of a 
semantic theory for DAML, since such a theory would make the meaning 
of 'equivalentTo' perfectly unambiguous. To keep things simple lets 
punt on the issues of whether an assertion is a global constraint, 
issues of who has the authority, etc., and just ask what the 
*content* of the assertion is. I can see in general terms how such a 
theory would go (based on the semantics for OIL), but the details are 
still a bit opaque. For example, consider the categories of Class, 
Thing and Property: do these overlap at all? Is a Class a kind of 
Thing? Can a Property apply to another Property? Things like that.

BTW,  DAML looks awfully like OIL (written in XML notation). It might 
also help if we could have a brief summary of where they differ.

Pat Hayes

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Received on Friday, 13 October 2000 12:57:55 UTC

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