Thanks to all who participated in this discussion -- David C, Mukul, David L, Len, Dan, Michael, Jim, John, and Ken.
Fascinating discussion!
For me the discussion has been a great reminder:
Schemas don't have any semantics.
I think that is something that bears repeating often.
I particularly like Jim Melton's definition of "optional":
Optional, in XML Schemas, in DTDs, and other
XML-related standards (at least within the W3C)
means nothing more than "may be provided or
omitted".
and he goes on to say:
Any "semantics" associated with the provision
or omission of something optional might be
provided by an application or other environment.
Awesome clarity!
At this point I will do my best at characterizing what I think Walter Perry would say:
The consumer of an XML instance document that
has an omitted element or attribute is free to give
whatever meaning he or she desires to that omission.
[Walter, if I have not accurately characterized your ideas please correct me.]
/Roger
