Another look at namespaces

[Rick Jelliffe]

From: Tim Berners-Lee <timbl at w3.org>
 >From: Rick Jelliffe <ricko at allette.com.au>
>
>>The only information that properly belongs in a namespace is a list of
>>names.
>
>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.

A name is useful by being available for use in a schema, document,
program, query, stylesheet or language. That use may be merely to
disambiguate
<rick:zzz/> from <tbl:zzz/> where these unique elements are only used
by a stylesheet to display some appropriate graphic.

"The namespace name, to serve its intended purpose, should have the
characteristics of uniqueness and persistence. It is not a goal that it
be directly usable for retrieval of a schema (if any exists)."
http://www.w3.org/TR/REC-xml-names/  s2

The spec clearly says that to be useful, a namespace URI does *not* have
to identifiy anything. It only has to provide uniqueness and
persistence.

The first paragraph of the namespaces spec begins:
"We envision applications of Extensible Markup Language (XML) where a
single XML document may contain elements and attributes (here referred
to as a 'markup vocabulary') that are defined for and used by multiple
software modules. "

Namespaces are concerned with vocabularies (lists with meanings, not
schemas: the words "schema" and "language" were available and were *not*
used).  Schemas are constructed from vocabularies.

>I have noone associated with W3C say that a "a namespace is a schema"

Err, isn't that your position above?   You say that a namespace cannot
be merely a list of names but must be "a language: a set of names plus a
set of syntactic contstraints" (sounds like a syntactic schema to me)
plus "a menaing shared by writer and recipient" (sounds like a semantic
schema).

Indeed your whole first posting to XML-DEV on namespace concerned
schemas and validity. "For example, you can run an xHTML document though
any
DTD you like if it suits your purposes, but if you want to
check whether it is valid xHTML then you should use
the xHTML schema which corresponds to the namespace URI."
If the namespace URI is a schema URI, then the namespace is a schema.

{In another posting}
>Perhaps perception of it is clouded by the fact that XML 1.0 doesn't
mention
>namespaces at all, and XML NS does not mention schemas at all.
>In other words, the specs -- having to only refer backwards in time --
>have not been good at pointing to how the future architecure will fit
>together.

No, perception is clarified by memories of how much effort and debate
it took to get mentions of schemas taken out of the Namespace document.

The early drafts were full of mentions of schemas. For example,
http://www.w3.org/TR/1998/WD-xml-names-19980327
even says "local schema namespace", combining them.  That the
XML NS does not mention schemas is by intent: to avoid mixing
up schemas and namespaces.  When the XHTML draft uses three
different namespaces for the same elements, it does just that.

I note Shane P. McCarron's recent post
"With regard to namespaces, IMO the work on Modularization is
orthogonal to namespaces."    If future modularized XHTML
does not conflate schemas and namespaces, what is the "future
architecture" that makes it so important to have three?

Rick Jelliffe


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