Re: How do you deprecate URIs? Re: OWL-DL and linked data

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