Namespace URI address resources

Rick Jelliffe ricko at
Wed Jun 16 03:39:37 BST 1999

From: Andrew Layman <andrewl at>

 >If we follow the principle of cleanly separating data from its
>we want firm ties to the definition of data, and loose ties to its

A schema is "processing" not "data": it is tied to whatever applications
understand the schema format. Editing, creating and validating against a
schema are all applications.

There is no schema language yet that can express all useful constraints.
To propose a mechanism that does not allow a plurality of schemas is, in
fact, to say that the schema language should defines the (bounds of the)
possible schemas: if XML-Data does not support a constraint, it  cannot
be part of schemas. This is putting the cart before the horse.

It is not that the namespace URI identifies a schema that it is the
problem, it is :

* the notion that a document has only *one* schema and
* there is no mechanism yet to allow alternative schemas to be assigned.

If W3C made a mechanism to allow alternative schemas (like Jonathon
Bordon's recent post), then the namespace URI could be overloaded to
provide a schema, as a defaulting behaviour in the absense of a PI. But
it is bad for the WWW if there is no mechanism to allow alternatives;
without such a mechanism, requiring overloaded use of the namespace URL
is bad.

Rick Jelliffe

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