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RE: "asserted triple" weasle-words must go [was: best way to write triples?]

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Thu, 18 Apr 2002 14:27:31 +0100
To: "Frank Manola" <fmanola@mitre.org>, <w3c-rdfcore-wg@w3.org>
Message-ID: <JAEBJCLMIFLKLOJGMELDEELICDAA.jjc@hplb.hpl.hp.com>
Jeremy:
> > Dark triples
> > [ ... ] are not in RDF M&S; they are not necessary; they do not clarify
> > M&S; they are not in charter.
> >
>

Frank:
> I'd like to see some amplification of the "they are not necessary" point
> before we make any decision on this.  The other points may be
> procedurally correct, but may be less important than the "semantics" of
> the issue (if you will).  For example, regarding the fact that they are
> not in M&S, presumably we're allowed to consider the new situations in
> which RDF may need to be used (e.g., supporting WebONT) that have come
> to prominence since M&S went to CR?  Even if we made a decision to drop
> this matter, I'd like to see us say something constructive about the
> issue of unasserted triples for the record (rather than just drop it as
> not being in charter).
>

My message reflected frustration I am feeling on WebOnt.

In DAML+OIL the syntax of the language is encoded *within* the model rather
than external to the model and merely interpreted in the semantics.

We see this too in RDFS consider:

A:
<my:range> <rdfs:subPropertyOf> <rdfs:range> .
<eg:foo> <my:range> <eg:bar> .
<a> <eg:foo> <b> .

The triples both map into the model, then within the model an RDFS
interpretation is constrained to understand the implicit triple "<eg:foo>
<rdfs:range> <eg:bar> ." and then that in turn constrains the interpretation
of the explicit triple "<a> <eg:foo> <b> ."
If we treated RDFS as merely a syntactic carrier then the fact that there
are not explicit <rdfs:range> triples in the original graph (A) means that
there are no range constraints to consider.

On WebOnt, Pat and Peter have both asserted that we need to use the RDF
graph as the syntactic carrier and not have such syntax reflected in the
model.

However, this assertion, while it is still being explored, currently appears
to me to be false. It seems possibly to encode the syntax within the model
theoretic interpretation (at least for webonts needs). I would like to see
examples where this is not possible (ideally in-charter examples).

In practice, nothing will stop people who want to treat the RDF graph
independently of its model theoretic semantics. However, *we* should, IMO,
not be licensing or encouraging such behaviour unless we believe it to be
advantageous.

I believe that such behaviour is disadvantageous, because it will mean the
extension mechansim available in RDFS, such as rdfs:subPropertyOf are only
applicable when people are using the model theory and not otherwise. Thus
these extension mechanisms will become a source of confusion, and fall into
disrepute. RDF document authors will need to know whether or not their
application is using asserted or unasserted triples.

The weasle words turn a normative specification into non-normative advice,
because anyone who doesn't like Pat's excellent work can simply say, "Ah,
but my graph isn't asserted"

Jeremy
Received on Thursday, 18 April 2002 09:28:23 EDT

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