Another look at namespaces

[Simon St.Laurent]

At 04:41 PM 9/15/99 -0400, Tim Berners-Lee wrote:
>The namespaces spec was adamant that you could use namespaces
>without having to dereference the namespace URI.
>However, as we define languages for talking about languages
>(XML and RDF schemas for example, even style sheets)
>the document corresponding to the namespace URI becomes
>the place where the namespace-author can put *definitive*
>information about the intent of the namespace.
>And this is not mandatory - but is very useful!

To me at least, this is at the heart of the technical aspects of this
issue.  In some cases, 'not dereferencing the namespace URI' is good - not
every processor is going to care what, if anything, is there.  

If we start to treat this as "You don't have to dereference it, but you
might find something interesting there", then we have to start talking
about what goes there.  The list of options, presented above, includes two
types of schemas plus style sheets, and there are _many_ more possibilities.

This approach is certainly plausible - it might match up with Jon Bosak's
earlier "provides for the creation of an XML Packaging WG when work on the
other specifications reaches a point where resources can be devoted to it"
- but it would help a lot to know what will be involved in that project and
how those dependencies affect current work.

Based on what's currently published, there aren't enough resources to make
this approach believeable, mostly because namespaces are described only as
identifiers. If namespace URIs are only identifiers, the approach described
above doesn't make sense.  If in fact namespace URIs will point to
something, preferably something machine-readable, it begins to make more
sense.

>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.
>You might of course have a local copy and not actually
>need to go onto the net to us live HTTP.

That sounds fine, but the DOCTYPE declaration already provides that
functionality, and XHTML 1.0 doesn't make clear any need for functionality
beyond that type of validation.  Namespaces and XML 1.0 validation, as I've
been reminded repeatedly on this list, have no necessary connection.
Future schema validation might make more sense, but we're missing some key
mechanisms....

>The exciting use of namespaces in schemas will be when we
>have schema documents which contain the syntactic
>constraints in xml-schema language, but themselves
>use other namespaces to come to express the
>entity-relationship model of data (rdf-schema),
>legally appropriate presentation (link to style sheet),
>financial implication (link to mapping to FSTC
>echecks or whatever).  The functionality which we
>will be able to build into new languages will grow
>as  the richness of languages to which we can map.

Is this all going into the schemas?  Or are we going to be building more
complete tools for describing document types by assembling lots of parts?
I hope (and it sounds like) the latter, but it isn't clear how we're going
to get there.

Simon St.Laurent
XML: A Primer (2nd Ed - September)
Building XML Applications
Inside XML DTDs: Scientific and Technical
Sharing Bandwidth / Cookies
http://www.simonstl.com

xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev at ic.ac.uk
Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1
To (un)subscribe, mailto:majordomo at ic.ac.uk the following message;
(un)subscribe xml-dev
To subscribe to the digests, mailto:majordomo at ic.ac.uk the following message;
subscribe xml-dev-digest
List coordinator, Henry Rzepa (mailto:rzepa at ic.ac.uk)