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Re: Proposed redefinition of "Property"

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 02 Jan 2001 10:01:22 -0500
To: david.silberberg@jhuapl.edu
Cc: www-rdf-logic@w3.org
Message-Id: <20010102100122O.pfps@research.bell-labs.com>
From: David Silberberg <david.silberberg@jhuapl.edu>
Subject: Proposed redefinition of "Property"
Date: Wed, 27 Dec 2000 15:28:47 -0500

> Hi,
> With that said, I am specifically questioning the definition
> of a property. Currently, properties are specified as
> "first class" definitions. The property itself specifies
> the domain resource and a cardinality. For example, a "parent"
> property is associated with the domain resource "Animal" with
> a cardinality of 2, meaning that an Animal can have 2 parents.
> However, there is nothing that restricts the domain of the parent.
> For example, one would want to restrict parents of Animals to be
> Animals. While there is a mechanism for doing this using the
> "toClass" property in the "restrictedBy" portion of a Class
> definition, it is somewhat awkward to break up the definition of
> a property like that. It would seem more appropriate to define
> the "toClass" in the property itself.

The association of domains, ranges, and cardinality with properties is
interesting and probably useful, but extremely non-modular.  I think that
it would place a very large hurdle in the merging or extension of

For a typical example of this, consider the problem that Ian Horrocks has
discovered with the DAML walkthrough.  In the walkthrough the property
``height'' is given domain ``Person''.  This has the effect that any
extension or merger of this ontology cannot use (this) height for any other
kind of object.  Yes, I know that you could use another height, but then
you would have two kinds of heights.

> What this does is remove some of the frame-based flavor
> of the DAML specification language, but it seems cleaner.
> I would be interested in other people's opinions on the
> matter.
> David

I don't care (much) about losing any possible frame-based flavour.  I do
care about losing other aspects, such as utility and modularity.
Unfortunately, many of these aspects have to be traded off against each
other.  (Actually, I do lean (technically) somewhat towards allowing
domain, range, and cardinality for properties, but I am very concerned
(operationally) with the increased possibility of creating ontologies that
are less useful that they could be.

Peter Patel-Schneider
Bell Labs Research
Received on Tuesday, 2 January 2001 10:02:06 UTC

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