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Re: Cyclic Classes/Properties [was: Re: DAML Correction: Same Is Not A Sub Of Sub]

From: Sigfrid Lundberg, Lub NetLab <siglun@gungner.lub.lu.se>
Date: Fri, 11 May 2001 13:39:25 +0200 (MET DST)
To: pat hayes <phayes@ai.uwf.edu>
cc: "Sean B. Palmer" <sean@mysterylights.com>, www-rdf-logic@w3.org
Message-ID: <Pine.LNX.3.96.1010511125901.18899H-100000@gungner>
On Thu, 10 May 2001, pat hayes wrote:

...

> The issue is being able to infer equivalence from other assertions.
> 
> >In other
> >words, if someone can come up with an practical real world example of
> >why cyclic classes should be introduced over equivalence (or why
> >cyclicity is required for equivalence... in Notation3!), then I would
> >be very glad to hear it.
> 
> Nobody (except you) is talking about these 'cyclic classes', whatever 
> they are. We are all talking about classes.
> 
> Pat Hayes
> 
> PS. You know, this little exchange is a lovely illustration of the 
> utility of a formal semantics. "Subclass"  sounds like it means 
> something, but exactly what it means needs to be spelled out in 
> mathematical terms to avoid needless misunderstanding.


I think that the problem here boils down to the wish to be able to say
things, and the wish to be able to infer things. I want to be able to say
that a sub-title is a subclassof title, and that there should be no doubt
whatsoever that all titles are not sub-titles. Just some titles are.

Some time ago, I was convinced by you (and other kind people on this list) 
that we do need a not-strict-sub-class-of. The cost of making certain
inferences be would far too high if we didn't. So I accept this... But I'm
not comfortable with it; aren't we trading inferability against
expressiveness? Aren't we enhancing the former at the price of the latter.
To put this in another way: Could the ability to say (i.e., in rdf/daml) 
that sub-titles "<" titles rather than just that sub-titles "<=" titles
make a more solid ground for inference. I mean, some statements could
actually be more precise... I'd reckon that we need both.


Sigge
Received on Friday, 11 May 2001 07:29:18 UTC

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