What is a namespace ... really?

david at megginson.com david at megginson.com
Fri Jan 15 15:10:59 GMT 1999

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 Megginson                 david at megginson.com

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