- From: Dan Connolly <connolly@w3.org>
- Date: Tue, 04 Sep 2001 16:30:57 -0500
- To: pat hayes <phayes@ai.uwf.edu>
- CC: w3c-rdfcore-wg@w3.org
pat hayes wrote: > > >Jan Grant wrote: > >[...] > > > While I have held, in principle, what I'd characterise as DanC's opinion > > > here (or the more extreme version: "alt is totally broken") > > > >I'm not saying it's broken; I'm just saying it's not magic. > >It's very mundane; from the MT perspective, > >it means no more or less than any > >other class (Apple, Bananna, Integer, ...). > > Then why bother even mentioning it in the M&S, let along spending > pages on it? For the same reason that C programming books mention printf(). Yes, everybody could develop their own print routine in vanilla C, but it's cost-effective for the community to agree on a standard library of terms sometimes. The widespread availability of printf() does not impact the syntax and semantics of the C programming language at all. It does, however, increase its utility significantly. > The M&S doesn't seem to feel a compulsion to go on and > on about recommended uses of Bananas. > > > > - that is, > > > that an app can infer what it likes, an alt-unaware MT is going to > > > produce an odd semantics for something like > > > > > > <doc1> <dc:creator> _:a . > > > _:a <rdf:type> <rdf:Alt> . > > > _:a <rdf:_1> <jan> . > > > _:a <rdf:_2> <dan> . > > > > > > ("doc1 was written by either jan or dan") - I don't see how you can > > > ignore alt in the MT and get this interpretation, no matter how you go > > > about it. > > > >I interpret that n-triples fragment not as "doc1 was written > >by either jan or dan" but > > > > doc1's has a creator value which is a collection including > > jan and dan; this collection is the sort where folks conventionally > >choose > > one from the collection, rather than using all of them. > > > >Again, suppose the graph had a Bag rather than an Alt: > > > > <doc1> <dc:creator> _:a . > > _:a <rdf:type> <rdf:Bag> . > > _:a <rdf:_1> <jan> . > > _:a <rdf:_2> <dan> . > > > >We don't license the inference that > > <doc1> <dc:creator> <jan>. > >in that case, do we? No. Then why should rdf:Alt have any magic > >associated with it? > > Because that is what the M&S seems to imply, seemed to me; and > because if we can't infer anything different from its being an Alt > than a Bag, why does the language have both constructs in it? At its core, the language has *neither* construct. It has only -- logical constants (URIs) -- existentially quantified variables -- two-place predicates -- conjunction That's it. Bag and Alt are just two logical constants. > It's > not a question of 'magic', but of understanding why there would be a > totally meaningless distinction built into the syntax. Just because the distinction is not specified in a model theory doesn't make it meaningless. The distinction between Apples and Bananas is not in the model theory, but there is a distinction: in many interpretations, their extensions are different. > This line amounts to treating all containers alike in the MT, exactly; which, I think, is why you were actioned to remove containers from the MT altogether. > ie they > are thingies that have elements which are accessed by applying rdf:_n > to them, and that's all. Yes! > The only differences between bags and seqs > and alts is that they are different by stipulation, ie nothing can be > both of them at once. > > However, if we do say this, then it seems question-begging (and > intellectually dishonest) to go on to say that some aspect of meaning > is 'conventionally' this or that, when the language itself doesn't > support that 'conventional' interpretation. In other words, we are > saying that it *does* mean something, nudge nudge wink wink, but *we* > aren't going to come out and say what it does mean, for some reason. Just not in the core model theory. > (Not that we couldn't: we can, in fact, but we are refusing to, for > some reason, probably because ... well, I cannot think why, to be > honest. ) > > This seems to me to be exactly the wrong way to set up a useful > semantic-web information interchange language. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 4 September 2001 17:31:01 UTC