X-Schema syntax

Paul Prescod paul at prescod.net
Tue Jun 29 00:38:02 BST 1999

Andy Dent wrote:
> I'm really not sure I understand what you're talking about here so
> the following comments may be totally inapplicable, but I think my
> point below is still valid.

Inapplicable but nevertheless intersting.

>  From a usability point of view (which drives a LOT of my API design)
> I think it is much easier for most people to understand definitions
> in context.
> Many document types, and particularly database documents, will define
> elements that are only meaningful in a larger context (eg: LastName
> within Person).
> The X-schema and DTD modes seem to support only defining all atomic
> elements separately from a context saying where they are used.
> This requires the reader and writer of these schemae to build an
> abstract model in their heads that puts the definitions in context.

There are not many elements that appear in one and only one context.
Therefore it is necessarily the case that readers must put definitions in
context "in their heads." When you see the definition for LI in HTML OL,
you need to keep in your head the fact that that same element type can
occur in HTML UL. If you define it in both places then you need some way
of saying that they are really the "same thing" -- the opposite of your
definitions in context.

If I had to choose, reusing element types (possible in DTDs) is more
important than being able to have locally named element types (just use a
local prefix!). In other words if I am required to choose I would have to
say that DTDs made the better of the two choices.

I don't have a big problem with contextually specific element types but
there are usuability issues there. Is it okay for you that dragging and
dropping a LastName from one context in a document to another would render
it invalid because the same tag means completely different things in the
same document? I'm not convinced that local element types are worth
causing this problem.

 Paul Prescod  - ISOGEN Consulting Engineer speaking for only himself

Those who profess to favor freedom and yet depreciate agitation, are men 
who want crops without plowing up the ground. They want rain without 
thunder and lightning. They want the ocean without the roar of its many 
waters. - Fredrick Douglass

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