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Re: Where DAML+OIL deviates from the RDF-Schema spec.

From: Tim Berners-Lee <timbl@w3.org>
Date: Sun, 4 Mar 2001 20:28:33 -0500
Message-ID: <00bf01c0a513$9bb02d70$c1defea9@CREST>
To: "Peter Crowther" <Peter.Crowther@melandra.com>, "pat hayes" <phayes@ai.uwf.edu>
Cc: <www-rdf-logic@w3.org>
DAML is in my opinion right.  If a is a subclass of b and b of a
mean that a and b are equivalent classes - this is not a bug.  You can't go
peperring the
underlying logical framework with exceptions just because in some cases
a loop is formed by mistake.

Yes, if you are in a GUI environment where people are expecting
to make a tree, it might by wise to alert the user that the subclass
relationship
they just entered makes  a bunch of classes equivelent. (Are you sure?)

In other practical cases the inference may be a useful operation of merging
subgraphs,
especially when different documents assert the two (or more) parts.
Part of the INS might assert that all Resident Aliens are Permanent
Residents
and another part assert the reverse, and the sysetem happily conclude that
they
share a common term. (If only standards were so easy! :-)

I don't know how you would make *local* rules to enforce the macroscopic
acyclic property - which is what you have to do in a scalable system. The
obvious
way is to insist that the Property not be used for equivalent classes, that
it be proper subclass.
To have a proper subclass relation as the only standard tool would be very
difficult - to have
not only to establish that every member of a was a member of b but also that
there was some member of b not a member of a?
Tim

----- Original Message -----
From: "pat hayes" <phayes@ai.uwf.edu>
To: "Peter Crowther" <Peter.Crowther@melandra.com>
Cc: <www-rdf-logic@w3.org>
Sent: Thursday, March 01, 2001 3:40 PM
Subject: RE: Where DAML+OIL deviates from the RDF-Schema spec.


> > > From: Dan Brickley [mailto:danbri@w3.org]
> > > I agree with [2] and [3], and could live with [1]. My main
> > > concern w.r.t.
> > > using loops in the class and property hierarchies to indicate
> > > synonyms is
> > > with end-user comprehensibility and with user interface
> > > generation.
> >
> >I suspect you end up having to implement loop detection in many systems
> >anyway.  Speaking from experience, provided you know you have to do it
it's
> >not a huge overhead for UI generation.  As for end-user
comprehensibility, I
> >also suspect [and hope] that most users will have editor assistance for
any
> >hierarchy that is complex enough to include loops.
>
> I think the issue is not the cost of finding them, but the inferences
> that it is proper to draw from them. Suppose A says that X is a
> remote sub-sub-.....sub-class of Y, and B says that Y is a remote
> sub-....class of X. Is this loop evidence of a confusion between A
> and B, or should a reasoning engine just happily conclude that A and
> B together imply thatX, Y and everything in between, are all the same
> thing? Right now, DAML does the latter.
>
> Pat Hayes
>
> ---------------------------------------------------------------------
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>
Received on Sunday, 4 March 2001 20:29:10 GMT

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