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Schemas: Different Strokes From Different Folks


Rick Jelliffe's recent article on xml.com,
sets the background for my question:

Rick raises the issue of "closed under union" and says:


According to James Clark "for any two RELAX NG schemas, there is a RELAX
NG schema for its union". Dr Murata's early research concerned set
operations on grammars, in fact. RELAX NG allows ambiguity during the
course of validation really well, until finally deciding whether the
document is valid, and so can support dialects well. Elegant and powerful.


But in Schematron, there is partial support for being closed under
union: if you use the phase mechanism you can certainly combine two
different schemas, but the language does not take care of the
disambiguation: you have to tell Schematron which phase should be
active: which patterns are in common whatever dialect is in and which
patterns only belong to a single dialect. In Schematron, the important
thing is to explicitly represent that you have these different variants,
not ignore them or necessarily handle them automatically.


There isn't a comment facility at so I'm posting here.

Perhaps my problem is with the use of "closed under union."

As I understand "closed under union," the result of an operation on a
set member must remain a member of the set."

I don't think it has anything to do with "...the language does not take
care of disambiguation: you have to tell Schematron..." Yes?

Hmmm, rather than saying two "different schemas," what if we said "two
different Schematron specified schemas?" Is a combination of those two
Schematron specified schemas a schema defined by Schematron?

If so, then are Schematron schemas "closed under union?"

Or was Rick's question about encountering two arbitrary XML schemas,
specified by some unknown means and then to be merged using Schematron?

The "partial support for being closed under union" was what originally
attracted by attention.

Glad to see XML.com is back up!

Hope everyone is having a great week!


Patrick Durusau
Technical Advisory Board, OASIS (TAB)
Editor, OpenDocument Format TC (OASIS), Project Editor ISO/IEC 26300
Co-Editor, ISO/IEC 13250-1, 13250-5 (Topic Maps)

Another Word For It (blog): http://tm.durusau.net
Homepage: http://www.durusau.net
Twitter: patrickDurusau 

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