W3C home > Mailing lists > Public > public-sw-meaning@w3.org > November 2003

Re: Meaning and context

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 05 Nov 2003 17:50:59 -0500
Message-Id: <200311052251.hA5MoxL6026575@roke.hawke.org>
To: Larry Masinter <LMM@acm.org>
Cc: public-sw-meaning@w3.org

> Meaning of terms comes not only from the terms but the
> context of use. While it would be preferable to have only
> a single meaning for a "URI" in all contexts, there are
> already sufficiently different contexts that it is impossible
> to define a single semantics for a URI without doing damage
> to one or another set of existing specifications from W3C
> or IETF.
> So, I propose that the community as a whole (W3C, IETF, etc.)
> adopt a context-dependent semantics. I believe that W3C
> specifications currently have different contexts of
> use for URIs which have different enough semantics to be
> called out:
> (a) "As a hyperlink"
>   This is the context used by <a href="URI"> and
>   <img src="URI"> and so on. The URI is being used as an
>   active link following the computational or operational
>   semantics defined by the (definition of the) scheme
>   of the URI used. That is, the only thing a "http"
>   URI can "denote" is the operational definition: it
>   denotes the result of the action of using the HTTP
>   protocol to the given host using the given path
>   in the protocol.
> (b) "As a concept identifier"
>   This context adds an implicit "thing described by"
>   level of indirection. URIs are used to denote the
>   thing that is _described by_ the resource that
>   is referenced by the URI used 'as a hyperlink'.
>   This is similar to what was intended by using "tdb"
>   in http://larry.masinter.net/duri.html. 

This all makes a lot of sense to me.   But...

> (c) "As an RDF concept identifier"
>   RDF seems to have bifurcated (a) and (b) by use of
>   the "#" fragment separator. URIs without fragment
>   identifiers are used to identify the hyperlinked
>   resource, while those with fragment identifiers are
>   used to identify the 'concept' that is described
>   by the resource. http://www.w3.org/ denotes meaning
>   (a), while http://www.w3.org/# refers to meaning
>   (b), the organization.

This is what it looks like, from a distance, but the RDF specs
themselves neither support nor advocate this approach.  It's just
something that some RDF users like to do.  The hash has as much
meaning in RDF as does the capitalization of the first letter (ie,
none to the machines).

I once proposed they make this split real [1], but RDF Core declined.
(More formally, as I recall, they simply didn't chose to decide
anything about it, in the days right before Last Call #1, and I never
raised it as a Last Call issue.)  Also, when I tried to implement it,
I found it rather painful, so since then I've focussed on how to live
with one shared context; I've found it surprisingly possible.  Some
notes near [2].

      -- sandro

[1] http://www.w3.org/2002/12/rdf-identifiers/
[2] http://esw.w3.org/topic/DualUseUri
Received on Wednesday, 5 November 2003 17:49:52 UTC

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