I do not like using them because there is
no way to know what the final content model is without some tool support. What
I don’t like is that looking at the content model I can’t tell that
a substitution is allowed. I have to track down all the elements that can be substituted,
without there being some flag on the head element to indicate substitutions are
being made. Sort of a good and bad point about them, is they also require all the
substituted values to be based upon the same type, this is not always a good
requirement.
Instead of this, ACORD has decided to live
with the minor namespace issues associated with redefine and prefer this
approach for extensions and restrictions.
..dan
From:
[mailto:]
Sent: Monday, August 29, 2005 3:40
PM
To:
Subject: [ubl] Substitution Groups
- Use 'em or lose 'em?
All,
We are
working on extensibility models for standardized business exchange
schemas. These schemas, under development by several standards organizations
make extensive use of hierarchical
schemas and namespaces, some of which
include schemas developed by third parties.
When a user or user community seeks to use these schemas, and, needs to
modify them in some way (without altering the underlying standardized
schemas), substitution groups can be a powerful and explicit mechanism for
such extensions and restrictions.
Several participants in these standard schema efforts have expressed reserve
from utilizing the W3C mechanism of substitution groups due to their
experience with non-uniform support of parsers for this schema feature.
In your experience, what are the concerns or recommendations on the
incorporation of substitution groups into the naming and design rules of
standardized schemas?
Should substitution groups be relied upon as an extension mechanism?
Marty Burns
Hypertek, Inc.
P +1(301)315-9101
E
