Names and schemas

Tim Bray tbray at
Mon Jun 1 18:38:39 BST 1998

At 10:14 AM 6/1/98 -0500, Steven R. Newcomb wrote:
>Using your defined terms, please
>explain the usefulness and/or purpose -- in terms of how it furthers
>the cause of reliable, vendor-neutral information interchange -- of
>declaring that a real or conceptual object exists, in the absence of
>any interchangeable definition of what that object is, or what
>constraints it must conform to in order to be processable.

No kidding.  Actually, the people I talk to worry more about rendering,
or running Java code on, said declared-but-opaque object, but validation
constraints are of equal importance.  My usual sound-bite on this is: XML 
makes it easy to invent a tag, but what's that buy you?  Nothing, unless 
you are willing to provide at least one of 

 (a) a stylesheet for rendering, and/or
 (b) some software to *do* something with it.

and if you want to support authoring or update, 

 (c) validation rules.

I think we can all agree that elements are not interesting without one
or more items from the list above.  

Having said that, namespaces all by themselves do have a couple of 
useful applications.  The most obvious, of course, is for software that
understands and knows how to deal with some particular element (e.g. 
MathML <Integral> or HTML <FORM>), and simply wants to run through
an otherwise-opaque document, find the elements he knows how to deal
with, and do his stuff.  Namespaces provide a reliable and robust way
to enable this.

I don't really agree with Paul Prescod's argument that the current 
namespace draft invades schema turf.  It does state that presumably
namespaces will in general have associated schemas (surely no-one here
disagrees?), but it bends over backward to avoid relying on the existence, 
availability, or format of these schemas.  At the moment, based on some 
off-line experimentation, I do think that the namespace facility will 
lend itself quite elegantly to the construction of partial composable 
schemas, the need for which is not in doubt. -Tim

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