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Re: RDF Semantics review: RDFS interpretations

From: Dan Connolly <connolly@w3.org>
Date: Thu, 13 Feb 2003 10:41:45 -0600
To: herman.ter.horst@philips.com
Cc: Pat Hayes <phayes@ai.uwf.edu>, www-webont-wg@w3.org, "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Message-id: <1045154504.8924.68.camel@dirk.dm93.org>

On Thu, 2003-02-13 at 05:03, herman.ter.horst@philips.com wrote:
> > On Thu, 2003-02-06 at 13:05, herman.ter.horst@philips.com wrote:
> > > RDF Semantics, version of 23 January 2003
> > 
> > Could you please summarize your review with one bit,
> > i.e. RDF semantics is acceptable or unacceptable
> > as is for use by WebOnt?
> In my previous message I summarized the status of my
> review, which is not yet completely finished [3].

Ah; sorry I didn't read more carefully...

> So I cannot yet give the one bit summary.

I see.

> > > The semantic conditions on rdfs:range and rdfs:domain
> > > do not yet incorporate an explicit domain assumption as just
> > > discussed.  It seems that additions such as the following need 
> > > to be made:
> > > 
> > > If <x,y> is in IEXT(I(rdfs:range)) 
> > > [then x is in IP and y is in IC] and 
> > > [if, in addition,] <u,v> is in IEXT(x) then 
> > > v is in ICEXT(y)
> > > 
> > > If <x,y> is in IEXT(I(rdfs:range)) 
> > > [then x is in IP and y is in IC] and 
> > > [if, in addition,] <u,v> is in IEXT(x) then 
> > > u is in ICEXT(y)
> > 
> > That seems substantive, but I'm not sure I understand
> > the problem. Could you state it as an entailment test,
> > please?
> (There is a typo in the second item: it should be domain instead
> of range.)
> These are omissions, which seem to be a remnant from the April 2002 
> version of the RDF MT, where the IEXT had all of IR as a domain.
> In the current version, something needs to be added.
> You cannot speak of IEXT(x) unless you assume that
> x is in IP.
> In both Peter's and my reading of the text, there should
> be the additions "then x is in IP" and "if, in addition",
> in both items.
> In "my interpretation" of IC/ICEXT, the assumptions
> "y is in IC" should also be added to both items.
> So here the Last Call text has an inappropriate omission 
> of a mathematical detail (a small error).
> I cannot relate this to entailment tests.

Hmm... maybe if I explain a bit?

An entailment test is just a very simple
	if P then Q
theorem. If there's a bug in the RDF semantics,
then we should be able to exhibit some
"if P then Q" theorem that, by design,
holds, but by the spec as witten, does
not hold... or vice versa... or at least:
where the answer to whether it holds or
not isn't sufficiently clear.

It's vitally important that substantive
technical issues get captured in this form.
It's just about the only reliable way to make sure
the deployed code matches the disposition
of the issue.

It also greatly facilitates group-to-group
communication. These tests leave very little
room for misunderstanding, matters of
taste/style, etc.

If there is no way to make this issue observable
as an entailment test, then I don't believe
it's a substantive issue.

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 13 February 2003 11:42:01 UTC

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