RE: some notes

Pat

> 1. Let's stop talking about what the meaning of a URI is, or might
> be. I suggest that the question is underdetermined, and cannot be
> answered sensibly, since 'meaning' can only be said to apply to
> larger pieces of representation than single words or URIs.

Of course. I have kept thinking and writing along those lines, but with not
much feedback here - maybe I don't speak loud enough, maybe my voice is not
one to be noticed against so many knowledgeable ones on this forum ... so
I'm happy to see this endorsed by a more authoritative one. Actually that
is something that techies know pretty well : a string means nothing outside
of a specific processing context ...

> We are being misled by the analogy with NL.  English words seem to have
> meanings all by themselves, in isolation as it were, but in fact
> those meanings are determined by a huge amount of surrounding
> knowledge and presupposition and shared beliefs.

Amen. A NL word is also a string (or a stream of sound is the exchange is
vocal). And the "shared knowledge" is the "processing context", no more no
less. This is not big deal, either - just common sense for techies, there
again. Anyone having tried to communicate with anyone else with neither
common language nor knowlegde has experienced the painful absence of
absolute meaning. This is something I've experienced a lot in teaching
maths :)

> Dictionary definitions are not really definitions in any foundational
sense:
> they are kind of sketches of a meaning which themselves rely on the
> same connected web of shared knowledge (some of it about language
> itself) which they set out to explain. URIs don't have this
> surrounding context of shared beliefs and so on; and in any case,
> URIs are not NL words.

Well, I won't be so definitive about boarders of NL. NL takes ages to build
up meaning through usage, and new forged names, and singularly technical
names, are for a while as meaningless to many people as URIs currently are.
But it may turn out that e.g. http://www.w3.org will make as much sense in
NL conversation to many users as W3C NL address (Street, Town, Phone number
...), and may be more than, say, "labeled hypergraph". It figures ... to
what extent do maths concepts belong to NL? Certainly "number" belongs to
NL, although it has not the same meaning for a 6 years old kid and a Ph.D.
in Algebra.

> In addition, it is notoriously hard to say what a 'meaning' really
> is, and there seems to be little point in this group diving
> head-first into a philosophical tar-pit as its first act.

Sure. As Peter pointed out, we are not to expect to solve those issues in
our personal lifetime - and certainly not even in our lifetime as a species
:))

So I think we should replace "meaning" by a more operational definition
like "behaviour in some processing context", and figure what are the URIs
processing contexts, and what is the behaviour expected in each of those -
maybe depending on the URI type or extension, as Sandro suggests.

> 3. Unfortunately, RFC 2396 has conflated two rather different
> relationships between a URI and a thing, viz. the 'identification'
> sense in which a URI provides access to a source on a network, as
> just outlined, and the 'denotes' or 'names' sense in which a URI is
> simply a name which denotes something in the, or even in a, world.
> This in itself would not be so bad, in fact, if we recognized that
> the first sense is a (very) special case of the second sense: after
> all, network sources are things in the world, presumably, and can be
> referred to.  But the RFC 2396 prose seems to be predicated on the
> assumption that these two relationships are *identical*, which is
> simply an error. It is a kind of colossal error, in fact, cosmic in
> its metaphysical scale and consequences; it imports a surreal fantasy
> into the very heart of the Web architectural theory.  Accepting it
> has led a number of smart people into making fantastical, nonsensical
> claims, such as that galaxies are 'on' the Web, or that the map is
> the territory, or that resources have no identity criteria, or that
> the act of typing a new a URI automagically brings a resource into
> existence.

Exactly, and well, sorry to hit on the same nail again, but Topic Maps
specification has clearly tackled this issue by making a clear distinction
between references to "subject address" (using the URI to identify the Web
source) and "subject indicator" (using the URI to identify the "world
thing" denoted by the source). And TM processors trigger different
behaviour out of that distinction, and avoid pretending Messier 51 is on
the Web.

> This conflation is seen in the strange uses to which this artificial
> word "resource" has been put, where on the one hand, we are told that
> resources are on a network, are uniquely identified by URIs (in fact,
> that it is a necessary truth that all URIs must identify a unique
> resource) and that the URI provides access to the resource, allowing
> operations to be performed on it: and yet also, that a 'resource' can
> be anything at all, including imaginary or Platonic entities,
> galaxies far, far away and things that are too small to count or
> identify.  This simply does not make any sense: it doesn't make sense
> to claim to provide access to perform operations on Julius Caesar or
> the Whirlpool Galaxy.  What does make sense is that the first set of
> conditions are appropriate and reasonable for the
> URI-identifies-network-source notion, and the second claim makes
> sense for the URI-denotes-entity notion. The craziness arises from
> thinking these are the same and that the same 'resources' are
> involved in both cases.

> I go over this stuff here (rather than the TAG group) because this
> regrettable confusion has permeated these discussions.  Since (it is
> claimed) a URI must identify a single resource - again, this does
> make sense in one reading, but we are now going to move to the other
> - that therefore all URIs must have a single *meaning*, and moreover
> that this single meaning must be fixed globally in all uses of the
> URI in all contexts.  This is bad enough: but this has taken even
> crazier form in the idea that this must mean that all URIs must have
> single denotation in all interpretations, a claim that is close to
> being incoherent, rather than merely wrong.

Yes. That would be like saying that "person" in NL is denoting only its
entry in Cambridge Dictionary - not even what is asserted in this entry,
but the entry itself. Completely absurd.

> (This is something of an aside, but a close reading of RFC 2396 and
> the REST documentation makes me suspect that the use of
> "representation"  there differs fundamentally from the way this word
> is used in semantics and KR work. I *think* - I would welcome
> correction if this impression is mistaken - that when REST talks
> about a representation of a resource, it means the sense in which for
> example the HTML emitted from a website is a representation *of the
> state of part of the Web server* at that address, rather than a
> representation of whatever the text of that HTML is in some sense
> 'about', eg astronomy, say, or liver disease. Similarly, if the web
> 'source' at that URI is, say, a live webcam, then the representation
> is a representation *of the state of the camera's phtoreceptors*, and
> hence of whatever the camera is seeing. In other words, this usage of
> 'representation' seems to be a relationship between a kind of
> snapshot of some network entity and the entity itself, or something
> physically attached to it rather closely, rather than a relationship
> between something like a text and whatever is described by the text.
> It is what has been called a grounded, 'direct', representation,
> fundamentally computational in nature; unlike a descriptive, semantic
> representation. If this is close to correct, it might go some way to
> explaining the terminological disconnects which seem to arise in
> these discussions, since these two notions of representation are
> obviously orthogonal.)

They are indeed, and both have to be taken into account. And there again,
in which processing context(s) does the URI mean the subject "directly"
represented (e.g. an application processing the image sent by the webcam),
and in which does it mean some abstract subject denoted or indirectly
represented (e.g. using dc:subject included in the same image metadata)

> So, the moral of this is, I claim, twofold: first, that we absolutely
> must keep these two distinct ideas clear in our discussions - that
> is, the network-maintained relationship between a URI and the
> information source that it identifies, on the one hand, and the
> semantic 'naming' relationship between a URI and whatever it might be
> taken to denote, on the other. Intuitions which are appropriate to
> one sense are quite inappropriate to the other.  Second, these two
> senses are, prima facia, quite independent: there is no particular
> necessary reason why a URI might not serve in both roles
> independently. So when talking about 'meanings', we need to be
> explicit about any relationships we might be presuming, or wanting to
> insist on, between these two senses.

Here we are. I forward this to Topic Maps community. I guess people there
will be very happy to read that, and hope some of them will join here.

(snip all the rest out of time and bandwidth to parse it thoroughly - sorry
about that).

Bernard Vatant
Senior Consultant
Knowledge Engineering
Mondeca - www.mondeca.com
bernard.vatant@mondeca.com

Received on Friday, 26 September 2003 05:05:51 UTC