Re: namespace usage as assertions

"Manola,Frank A." wrote:
> 
> This is probably a really dumb question at this point in the discussion,
> but as it relates to the RDF model of assertions being attributable to
> individuals, I'd like to get the point nailed down.
> 
> To wit:  isn't it the case at the moment that, since the URIs that
> identify namespaces may actually point to nothing,

That's not the case. Every URI, by definition, identifies/points to a
resource.
URI means "Uniform Resource Identifier"; URIs identify resources.
cf RFC2396 for the exact definition.

> the most you can say
> about using such an identifier is that it's an assertion (by the user)
> that there is a namespace identified by the URI, and that the namespace
> contains the specified element name(s)?

You can certainly say those things, but those are not the only
things you can say.

In particular, if the user chose a namespace name beginning
with http:, you can infer that a description of/representation of
the resource identified by that URI is generally available on demand.

(I say generally because this is a distributed system,
and availability isn't guaranteed)

It's a matter of dispute whether the resource identified
by the URI is the same thing as the namespace identified
by the URI, but how HTTP URIs work is standardized.


> In other words, since there's not necessarily anything "at" the URI that
> defines the set of names in the namespace independently of what is
> stated in documents that might refer to the URI (documents which might
> be created by many different people), there's no way to tell if a given
> use is actually correct in asserting that a name is part of a
> namespace.  For example, if userA says
> 
> xmlns:x="http://foo"
> 
> and then says
> 
> <x:Title>
> 
> there isn't necessarily a way to independently verify that there really
> is such a namespace that includes the name "Title".  All you may be able
> to know is that the user has made that assertion.

True, there isn't necessarily a way. But I expect that in many
cases, there will be a way, and I think that cases where there is
no way should be avoided.

For example, if userB writes

	<html xmlns="http://www.w3.org/1999/xhtml">
	<banana/>
	</html>

then userC can, independently, access http://www.w3.org/1999/xhtml 
to get an HTML document that says that the use of that namespace
name is governed by the XHTML 1.0 specification, look in that
specification, and discover that there is no 'banana' element
in the XHTML namespace at this time, and that every html element
must contain a head and a body.

In due course, an XML schema may become available from that URI,
at which point the discovery that this document conflicts with
the namespace name issuer's intended usage can be automated.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/

Received on Wednesday, 21 June 2000 13:07:23 UTC