xml-dev - Re: simple question on namespaces. Last one.

[Paul Tchistopolskii <paul@qub.com>]

From: Andrew Layman <andrewl@microsoft.com>


> 1. a. The URI of a namespace is not a mere string.  Per the namespaces
> in XML specification, it is a URI.

A.  ... every W3C namespace is not just URI, but it is URL ...

Is it on purpose ? OK, let's keep that http: , but use
http://w3c.org:something:here

Why W3C makes all their namespaces URLs but not URIs ? -
that was my question.

B. Why it should be URI ? What is the rationale for this self-limitation ?

> 2. a. Retrieval of a document or other resource based on the URI
> of the namespace is not "abuse" of the specification.  The specification
> states "It is not a goal that it be directly usable for retrieval of a
> schema (if any exists)."  Had it been the intention of the specification's
> authors to prohibit retrieval of a resource, the wording would have said
> that, instead.  As it is, the specification is simply neutral on the matter
> of whether retrieval is possible or not, desirable or not.

It is the problem that it is neutral. This mean that tool X that will start fetching
schema ( or *god-knows-what* ) will be conformant to this specification.

What is 'neutral', by the way ? I have a feeling that all the books / materials
on  XML I've seen are not  *that*  neutral.

########################

Current tutorials on XML are explicitly saying things like :

Michael Kay: ( page 733 )

Namespace URIs are unusual in that there is no actual resource
that can be obtained using the URI; the URI is simply a unique
identifier. In practice, any string can be used as a namespace URI
though "http://" URLs are often used to give some prospect of
uniueness.

http://tech.irt.org/articles/js193/index.htm

"The namespace is identified by a URI, either a Uniform Resource Locator (URL), or a
Uniform Resource Number (URN), but it does not matter what (if anything) it points to.
URIs are used simply because they are globally unique across the Internet, and thus help
produce identifiers that are universally unique. "

http://msdn.microsoft.com/xml/tutorial/use_namespaces.asp

What is an XML namespace?
An XML namespace is a collection of names that can be used as element or attribute names
in an XML document. The namespace qualifies element names uniquely on the Web in order to
avoid conflicts between elements with the same name. The namespace is identified by some
URI (Universal Resource Identifier), either an URL (Uniform Resource Locator), or an URN
(Uniform Resource Number), but it doesn't matter what, if anything, it points to. URIs are
used simply because they are globally unique across the Internet.

##########################


I think almost every explanation of namespaces will tell that
"there is no actual resource that can be obtained using the URI"

This is because every novice when he looks at any W3C namespace
asks himself : "what is this URL about?"

People are confused with this practice of W3C and those who are writing
about namespaces are trying to tell people that : "namespaces are
using URLs just for uniqueness - there is nothing associated with
those URLs"

And now you are saying that "spec is neutral". Poor XML evangelists,
they'l have to rewrite all they books, after tool X will start abusing
"neutral specifcation".

I agree that 'abusing' could be considered a bad word, because
it is impossible to abuse the "neutral specification".

> 3. I do not understand what you are saying in this point.

> 3. I'm  XML developer. I have to design some schema
> and I also want my documents to be processed by tool X.
> Of course - I'll use URLs for my namespaces , so that tool
> X can work with my 'namespaces'. Why should I take
> something *other* than URL ? URL is fine with
> W3C paper. URL is fine with 'tool X'. - very good.

What is not clear ?

- There is some popular tool X which is attaching the new semantics
to the namespace name,  (  ==  tool X is using namespace names
as URL for fetching god-knows-what  )

- I am a developer who is thinking about the name for *my*
namespace. I know that tool X has a feature (1).
I'l of course make my new namespace a URL ( not URI ).
Just in case.

What is not clear ?

> 4. I do not understand what you are saying in this point.
>
> I do not understand the somewhat conspiracy-theory like discussions of "tool
> X."

I suggest you'l make an experiment.

Assume that you wrote some tool ( let's call it A if you don't like 'X' ) which  is
working in assumption that every namespace declaration in any XML document
is a URL pointing to some Schema file.

Assume that I  wrote some other tool ( let's call it B ) which  is
working in assumption that every namespace declaration in any XML document
is a URL pointing to some RDF file.

Try to use both A and B. See that it is not possible.

OK, so the solution to this problem is W3C stepping out and saying
that : "Those URIs are URLs and they should point to: ..." ?

> One last point: During the namespaces specification design and also during
> the design of schemas, it was lengthily debated whether a namespace and a
> schema are coextensive, that is, whether there is only one schema associated
> with a namespace and visa versa.  In both cases, the conclusion after much
> consideration was that namespaces and schemas are distinct.

Very good. So W3C will  *not* step out and will  *not* say that. Right?

Good for tool X. It will become a de-facto standard.

What is 'conspiracy' ?

Anyone can make this 'what if' experiment and see what will happen after
some popular tool will start fetching document by 'namespace' URL.

*no* matter what will be that document - it will become a de-facto standard.

Rgds.Paul.