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

Meaning and context

From: Larry Masinter <LMM@acm.org>
Date: Wed, 05 Nov 2003 13:51:52 -0800
To: public-sw-meaning@w3.org
Message-id: <002701c3a3e7$05a3a750$bf422099@MasinterT40>

From the last teleconference, I was asked to write up my point
of view. 

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. 

(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.

Concept identifiers (b) are used, in their own right,
within ontologies, where communities of use agree
to use _the same_ URI within the community, by establishing
web resources (or imagining that one might establish
a web resource) and then using its URI to refer to
the concept.

For example, the context of "XML namespace name"
that appears inside xmlns="URI" within XML is
as a particular kind of concept (a 'namespace').

Note that the above theories of meaning (a)-(c) do
not depend in any particular way on 'owners' or
'authorities' establishing meaning; the reader or
receiver of a communication that contains a URI doesn't
need to know who the authority is or what they might
have said at some time in the past in order to be
able to interpret the URI.

Context (b) (and by derivation, context (c)) do
have communities of practice around them, but they
are not necessary in order to create meaning.

It is necessary to at least have (a) and (b) if
you want to use 'http:' URIs in some contexts to
refer to abstract concepts, because there is no
way to ever shake off meaning (a). If you want a
'http:' URI to be able to talk about your car,
then you still need some way of talking about the
resource of "what you connect to via HTTP" that
is different from "your car". It is inescapable.
There's no way to do the 'lifting' without a
'lift' operator.

http://larry.masinter.net  <- my web page, not me.
Received on Wednesday, 5 November 2003 16:53:44 GMT

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