XML trade off 1 - DTD vs XML Schema

Rick Jelliffe ricko at allette.com.au
Tue Jul 27 18:27:58 BST 1999

From: Mark Birbeck <Mark.Birbeck at iedigital.net>

>Don Park wrote:
>> > document - you just pass a 'sub-set' of the schema (which is still
>> > itself a valid schema).
>> Thus we end up with "XML Schema Fragment" (XML Schema + XML
>> Fragment).  Has
>> anyone actually tried doing this?  I am interested in knowing
>> any serious
>> issues.
>Er ... no you don't. (It might be worth revisiting the raging debate
>about fragments from a few months ago.) The technique I have used means
>it is always a complete schema, if it only represents a sub-set of some
>larger schema.

So does the recipient system look through the document and then
request a schema server for the appropriate minimal schema to be
generated and sent, or does the server already have a separate schema
generated for each instance?

Last year I proposed that it would better to allow downloading
of schema fragments on an individual name basis: the XML-Bind
proposal was to allow a kind of link from element types to
resources. This would be a practical way to implement this kind of
thing. The same mechanism would allow non-schematic links,
such as default values for attributes, which are troublesome in
XML Schemas. The latest XLink almost allowed links based on
types (making the "from" and "to" attributes on arcs point to
type names would allow this), but they have currently disallowed it
again unfortunately.  I hope they swing back to allowing it

Rick Jelliffe

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