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Vagueness vs. ambiguity [was Re: Editor's Draft of ISSUE-57 URI Usage Primer]

From: David Booth <david@dbooth.org>
Date: Fri, 19 Oct 2012 23:02:07 -0400
To: "Henry S. Thompson" <ht@inf.ed.ac.uk>, Alan Ruttenberg <alanruttenberg@gmail.com>, www-tag <www-tag@w3.org>
Message-ID: <1350702127.27835.16703.camel@dbooth-laptop>
Sorry for the long delay (due to travel) in following up on this.  Henry
Thompson raised this point, and Alan Ruttenberg did also, so I thought I
should address it.

On Wed, 2012-10-10 at 12:17 -0400, Alan Ruttenberg wrote:
[ . . . ]
> It seems clear that you are confusing ambiguity and vagueness. It
> seems to me that before you continue making further assertions about
> ambiguity in this context, you should understand and integrate this
> into your thinking.

Good point.  Indeed, philosophy distinguishes between ambiguity and
vagueness:
http://plato.stanford.edu/entries/ambiguity/
"Ambiguity is generally taken to be a property enjoyed by signs that
bear multiple (legitimate) interpretations."
http://plato.stanford.edu/entries/vagueness/
"Vagueness is standardly defined as the possession of borderline cases."
(And thanks for sending that link in your private email.)  

For example, a case of ambiguity would be the use of a URI to refer both
to a web page and to its subject (presuming its subject is not the web
page itself).  Whereas a case of vagueness would be the use of a URI to
refer to Mount Everest, as a physical object, because it is not clear
where its borders should be drawn, so different parties might make
different assumptions about where they should be drawn.  (Thanks to Pat
Hayes for this example.)

But the context of the issue-57 discussion is not philosophy, it is the
RDF / Semantic Web use case, which is about machine processing.  And
AFAICT, in this context the net result is the same: ambiguity and
vagueness both lead to RDF being written that makes different
(potentially conflicting) assumptions about the properties of a URI's
denoted resource, and this causes such RDF to be unusable by
applications that need to distinguish between those resource identities.
For example, an application may be unable to produce correct output if
the license terms are ambiguously attributed to both a landing page and
its subject, just as a different application may be unable to produce
correct output if the mass of Mount Everest is ambiguously attributed to
both Mount-Everest-whose-borders-are-here and
Mount-Everest-whose-borders-are-over-there.

I can see that the social processes for reducing the ambiguity or
vagueness may be slightly different.  In the case of vagueness, one may
have to decide how to quantize borderline cases into distinct resources
before assigning separate URIs to them, whereas with ambiguity there's
an assumption that the resources are already distinct, and merely need
different URIs.  But in both cases, the URI definitions need to define
these distinctions.

Regardless of how carefully a URI owner attempts to define the URI's
referent, it is always possible -- except perhaps in rare cases such as
purely mathematical definitions -- to come up with finer distinctions
that the URI owner never anticipated, does not know and may not even
understand or care to understand.  AFAICT, once this limit is reached
the cause -- whether ambiguity or vagueness -- seems irrelevant.

Do you agree?  If not, what difference in impact do you see?


-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Received on Saturday, 20 October 2012 03:02:36 GMT

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