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Re: Summary and some analysis: New Semantics Initiative

From: patrick hayes <phayes@ai.uwf.edu>
Date: Fri, 14 Jun 2002 10:31:35 -0500
Message-Id: <p05111a05b92fba804423@[]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org

>Here is my summary of the new semantics initiative as I understand it so far:

Wonderful job. Only one tiny addition needed, and that hasn't been 
said before clearly:

>There are two separable issues being discussed under this title:
>   o using a melange of model theories to define the semantics of SW 
>languages isn't going to work, as demonstrated by webont
>   o a mechanism for darkening some triples in a non-monotonic way.
>I muddied the waters by introducing the second into this thread. 
>That was a mistake.  This summary is just about the first issue.
>It is proposed to produce a W3C note which outlines a strategy for 
>defining the semantics of SW languages in terms of Lbase, a 
>representation of FOL.
>A new deliverable by RDFCore WG is proposed.  This will define the 
>semantics of RDF in terms of Lbase.  It is proposed that this 
>document is in addition to the model theory document and will define 
>exactly equivalent semantics to the model theory.
>This proposal is motivated by a concern that:
>   o model theory is hard:  it will take a lot (more than available) 
>of expert effort for each SW language to define its semantics as a 
>model theory
>   o it is not clear how the model theories of multiple SW languages 
>can be combined to provide a clear semantics for mixed language 
>The proposed new document is expected to have minimal effects on the 
>content of the RDF/XML syntax doc, the primer, the RDF schema doc 
>and the test cases doc and only minor effects on the model theory 
>It is suggested that it is important to include this new deliverable 
>in the current round of deliverables by RDFCore so that it has 
>normative status enabling other WG's (webont?) to build on it. [I'm 
>not sure about this one - see below]
>It is suggested that this new form of representing the semantics 
>will be easier for folks to understand.
>Jos has tested the new proposal in Euler and found no bugs.
>It is suggested that this is a harmless change; if it isn't adopted 
>by say webont, it will still do some good and no harm.
>I have spoken to some of the webont folks here, (Horrocks, PFPS, van 
>Harmlen) and got a mixed response.  One criticism is timing; a 
>concern that layering is a deep and hard issue that needs careful 
>consideration, not rushing in at the last minute.

Good point, but its important to note that this isnt being suggested 
as a final solution to all the worlds layering problems. There are 
still sensitive issues about how to map different languages into 
Lbase in ways that are mutually consistent, for example. But what it 
does do is provide a much more 'open' and semi-machine-checkable 
framework in which to do the work, as it were. Layering still is 
going to have to be done by craftsmen, but this is a better workshop 
(more light, some machine tools :-).

Second, although we are indeed rushing at the last minute to get this 
at least referred to by the RDF draft REC, for essentially political 
reasons, the ideas aren't rushed or last-minute. In fact, to fess up 
completely, none of my friends will be surprised to know that I, for 
one, have been thinking in these terms from day one, but I didn't 
express it that way because, well, I didn't thing the world was ready 
for it yet.

>I assume that the proposed new document is not normative as it is 
>based on Lbase which is defined in a note.  Is this a problem?

I honestly do not know, but I bet it can be got around by careful 
choice of wording.

>  At least it ducks the question of which is right if the axiomatic 
>and model theory semantics disagree.

Indeed. I would be quite happy for the RDF MT to be the normative 
document, if that is considered an issue.

>I have a number of process concerns about this, in particular I 
>would like to ensure that the whole community expert in this issue 
>is involved working it out, but that doesn't sound like a good thing 
>to do to RDFCore right now.

We havn't pitched it to Webont because that didn't seem so urgent, 
and there are only 30 hours in the day. But I don't expect to find 
serious opposition to the basic idea. In many ways it is similar in 
spirit to the 'axiomatic semantics' done for DAML, and that is more 
popular than the DAML MT. There may be some niggling over the 
details, of course.


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Received on Friday, 14 June 2002 11:31:37 UTC

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