Another look at namespaces

[Tim Berners-Lee]

-----Original Message-----
From: David Megginson <david at megginson.com>
To: XML-DEV <xml-dev at ic.ac.uk>
Cc: Tim Berners-Lee <timbl at w3.org>
Date: Friday, September 17, 1999 3:23 PM
Subject: Re: Another look at namespaces


>Tim Berners-Lee writes:
>
> > That is not useful.  I realize that the word "Namespace" (as the
> > end result fo the discussions of modules or docuemnt types or
> > vocabularies or...)  may be an english word which does not convey
> > this, but a a namespaces is a language: a set of names plus a set
> > of syntactic constraints plus - to be useful - a meaning shared by
> > writer and recipient.
>
>As (I think) Tim is arguing later in his message, a Namespace is a
>component of a vocabulary: specifically, it's the mechanism that XML
>documents use to represent (and disambiguate) the names that are part
>of a vocabulary, but, as Rick argues, it's not the vocabulary itself.
>
>Since Paul Prescod mentioned Chomsky, I'll mention Saussure: like
>written or spoken words, a namespace-qualified name is a pure <foreign
>lang="fr">signifiant</foreign> without any <foreign
>lang="fr">signifiée</foreign>.



There is a signifiée, unless the namespace is useless.
To design a namespace with no meaning is a possible excercise
but as documents written in such a namespace would have no meaning.

The namespaces spec doesn't tell you how to describe the
meaning of a name. But that does *not* mean that it should have none.

>For example, the signifier "{http://www.megginson.com/ns/}apt" can be
>represented by Namespaces.  The signified (say, "a valid ICAO airport
>code") cannot be represented by Namespaces, but for now will probably
>be represented in human-readable documentation and hard-coded in
>applications.
>
>I guess that a machine-readable schema could constrain the element to
>contain up to four alphanumeric characters, but who cares, really?

> My
>application still has to know somehow that it's an airport code and it
>has to know what it wants to do with airport codes (sell you a ticket?
>give you driving directions? tell you that the document contains a
>match for the code you were looking for?).


But once your application can do that with a
http://www.megginson.com/ns#element-apt
then an RDF assertion that

http://www.blee.com/ns2   is-subset-of    http://www.megginson.com/ns

will allow your application to know automatically
how to process airport codes in my vocabulary.
I just declared mine to be a subset of yours.

Or I might in a schema want to assert that
http://www.blee.com/ns2#element-airportcode is-equivalent-to
http://www.megginson.com/ns#element-apt

>David

Tim



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