- From: Richard H. McCullough <rhm@PioneerCA.com>
- Date: Wed, 9 Jul 2008 19:07:10 -0700
- To: "Booth, David \(HP Software - Boston\)" <dbooth@hp.com>, <martin.hepp@uibk.ac.at>, "Giovanni Tummarello" <giovanni.tummarello@deri.org>
- Cc: "Jonathan Rees" <jar@creativecommons.org>, "Bernard Vatant" <bernard.vatant@mondeca.com>, "semantic-web at W3C" <semantic-web@w3c.org>, "Earle Martin" <earle@downlode.org>
I'm glad you brought up Pat Hayes' possible worlds semantics. I think that is very important, and very wrong. But I don't want to say any more than that, until after I have read the paper which you have referenced below. Dick ----- Original Message ----- From: "Booth, David (HP Software - Boston)" <dbooth@hp.com> To: "Richard H. McCullough" <rhm@PioneerCA.com>; <martin.hepp@uibk.ac.at>; "Giovanni Tummarello" <giovanni.tummarello@deri.org> Cc: "Jonathan Rees" <jar@creativecommons.org>; "Bernard Vatant" <bernard.vatant@mondeca.com>; "semantic-web at W3C" <semantic-web@w3c.org>; "Earle Martin" <earle@downlode.org> Sent: Wednesday, July 09, 2008 6:29 PM Subject: RE: How do you deprecate URIs? Re: OWL-DL and linked data > Hi Richard, > > It sounds like we may be talking about different problems, or perhaps > different use cases. I'll try to clarify what I (and I think Martin) > meant in my comments about owl:sameAs. > >> From: Richard H. McCullough [mailto:rhm@PioneerCA.com] >> >> I haven't been following the "deprecate URIs" thread, so >> forgive me if I'm being repetitious. >> 1. everything is contextual. But that's no excuse for being >> sloppy with meanings. > > I agree that sloppiness is bad, and did not mean to imply that it should > be sanctioned. But "sloppiness" is also a value judgement that depends on > the application -- one person's simplicity is another's sloppiness -- and > it's important to have strategies for dealing with it when it does occur. > >> 2. ambiguity is not inevitable -- it is avoided by clearly identifying >> context. > > It depends what you mean. If you are talking about determining the real > world referent of a statement (step 2 in slides 5-8 of > http://dbooth.org/2008/irsw/slides.ppt ), then as Pat Hayes has pointed > out several times, completely nailing that down is almost always > impossible. And trying to pin it down by clearly identifying context > won't help: that merely begs the question of how to unambiguously identify > the context. See Pat Hayes' and Harry Halpin's paper "In Defense of > Ambiguity": > http://www.ibiblio.org/hhalpin/homepage/publications/indefenseofambiguity.html > > On the other hand, if you are talking about determining the set of > assertions that constrain a statement's meaning within semantic web > architecture (step 1 in slides 5-8 of > http://dbooth.org/2008/irsw/slides.ppt ), then I agree that can be > unambiguous. > >> 2. OWL:SameAs (like mKR:is) means identical -- two names >> (aliases) which >> mean the same thing. Let's not corrupt the meaning of this term. > > Agreed. We should not change the semantics of owl:sameAs. > >> 3. there are other terms which can be used to express varying >> degrees of similarity. > > But owl:sameAs is *exactly* the term needed to indicate that both a:a and > b:b denote the same resource in a statement like this in File1: > > a:a owl:sameAs b:b . > > or that b:b and c:c denote the same resource in a statement like this in > File2: > > b:b owl:sameAs c:c . > > However, that does *not* mean that an application X wishing to combine the > data from File1 and File2 must treat a:a and c:c as denoting the same > resource. Indeed, doing so may cause a logical contradiction. > > What's going on? From the File1 author's perspective, a:a and b:b denoted > the same resource, and from the File2 author's perspective, b:b and c:c > denoted the same resource, but from X's perspective, they may not. One > may ask, "what resources are a:a, b:b and c:c *supposed* to denote?", but > their definitions may well admit multiple interpretations, and multiple > interpretations are permitted in the RDF semantics: > http://www.w3.org/TR/rdf-mt/#interp > [[ > The basic intuition of model-theoretic semantics is that asserting a > sentence makes a claim about the world: it is another way of saying that > the world is, in fact, so arranged as to be an interpretation which makes > the sentence true. In other words, an assertion amounts to stating a > constraint on the possible ways the world might be. Notice that there is > no presumption here that any assertion contains enough information to > specify a single unique interpretation. It is usually impossible to assert > enough in any language to completely constrain the interpretations to a > single possible world, so there is no such thing as 'the' unique > interpretation of an RDF graph. > ]] > > One may be tempted to claim that the File1 and File2 authors overstepped > their authority in further constraining the permissible interpretations of > a:a, b:b and c:c to the extent that they were then able to assert them as > owl:sameAs each other. In other words, it may be tempting to claim that > those authors should not have further constrained the interpretations of > a:a, b:b and c:c beyond the terms' original definitions. But the fact is > that virtually *every* assertion involving the term, beyond the logical > entailments of a term's definition, further constraint the permissible > interpretations for that term. > > So the problem is not that owl:sameAs has been abused, nor is it that the > assertions in File1 or File1 are "wrong". The problem is that the models > of the world embodied by the assertions in File1 and File2 are mutually > incompatible: they cannot be used together in application X without some > surgery. And the point of slides 15-17 in > http://dbooth.org/2008/irsw/slides.ppt > is to describe one technique for performing such surgery when it is > needed. > > So if indeed "It is usually impossible to assert enough in any language to > completely constrain the interpretations to a single possible world", as > stated in the RDF Semantics, then the logical consequence is that > ambiguity is inevitable, so we may as well get used to dealing with is. > > On consequence of this is that there is a practical trade-off between > reusability and precision: the more precise a term, the more constrained > it is, and hence the more "likely" it is to be incompatible with other > assertions. Of course, people do not choose assertions at random, so we > cannot really view this as a simple probability of incompatibility, but > the trade-off is nonetheless real: all other things being equal, more > constraints means less reusability (without requiring surgery, at least). > > On the other hand, having too few constraints makes a term useless in a > different way, when nobody can figure out what it means. So defining > good, reusable terms is a balancing act: the best terms are those that are > constrained enough (and in the right ways) to be useful, but not so > tightly as to preclude too many applications. There is no substitute for > good judgement. > > > > David Booth, Ph.D. > HP Software > +1 617 629 8881 office | dbooth@hp.com > http://www.hp.com/go/software > > Statements made herein represent the views of the author and do not > necessarily represent the official views of HP unless explicitly so > stated. > > > Dick McCullough http://mKRmKE.org/ Ayn Rand do speak od mKR done; knowledge := man do identify od existent done; knowledge haspart proposition list; mKE do enhance od "Real Intelligence" done;
Received on Thursday, 10 July 2008 02:17:59 UTC