[Bug 6021] Stylesheet for xs:override

http://www.w3.org/Bugs/Public/show_bug.cgi?id=6021


Noah Mendelsohn <noah_mendelsohn@us.ibm.com> changed:

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                 CC|                            |noah_mendelsohn@us.ibm.com




--- Comment #3 from Noah Mendelsohn <noah_mendelsohn@us.ibm.com>  2008-09-12 20:19:36 ---
Michael Kay writes:

> More seriously, I think there is a big usability problem with this
> mechanism.  If you are trying to define a local variant of a complex
> schema (say FpML), then it won't be possible to override definitions
> in any module (schema document) of that schema other than the
> top-level module. For example, if the base schema has a typical
> structure with a root module schema.xsd that includes many other
> modules a.xsd, b.xsd, c.xsd (many of which probably include another
> module called lib.xsd), then it's hard to see how a customisation
> layer can override a definition in b.xsd or lib.xsd. If you attempt an
> xs:override of that module, you will end up with an inconsistent
> schema that contains both the original and overridden versions of the
> component.

I think it's worth observing that mechanisms that override or redefine at the
component level are more likely to be effective in cases where multiple modules
(schema documents) are composed and the intention is to further refine or
override the definition resulting from that composition.  Regardless of the
details, doing this in a stylesheet seems to require a transform that operates
on all of the input modules, and that to some degree reconstructs the partial
orders and derivation chains the result from composing such modules.  By doing
redefine and/or override at the component level, one at least has the
opportunity to define the override operation in terms of the existing rules for
composing the other input modules.  (and I grant that those rules aren't
currently as clear as we'd like them to be.)

I am not specifically asking to reopen the decision to adopt a source-transform
based override mechanism, though I have always had my doubts that it is the
best way to go.  If it some point a decision is made to reconsider the
composition story, I hope careful consideration will be given to the tradeoffs
involved in going with source-based vs. component-based approaches (and I do
think there are advantages to each.)

Noah


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Received on Friday, 12 September 2008 20:20:11 UTC