What is a namespace ... really?

[david at megginson.com]

Borden, Jonathan writes:

 > This is the *current* state of affairs. There are people who also
 > believe that in the future the namespace concept is to be extended
 > to incorporate Schema definition. That is, when a namespace URN
 > points to a Schema definition, the Schema may, can or will be
 > enforced in the same way that a DTD is enforced by a validating
 > parser and a <!DOCTYPE definition.

Ack! No!  Please don't hardcode a one-to-one relationship between
schemas and namespaces.

A single schema could define structures using elements and attributes
from more than one namespace, and elements and attributes from a
single namespace can be used and structured in many different ways.

SGML people handle this problem in a fairly clumsy way by using public
identifiers for indirection and then swapping entity catalogues at
different stages of production.  We can do better if do what a
database designer does for many-to-many relationships: add separate
associations between the namespace and the schema.

The alternative would be to rely on HTTP content negotiation to get
the kind of schema you want, and that is a pretty grim prospect
(especially for people with web sites hosted by large ISPs who really
aren't going to let them fiddle with the web server).


All the best,


David

-- 
David Megginson                 david at megginson.com
           http://www.megginson.com/

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