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Re: [xml-dev] a puzzling schema promise

Yes, it does not seem right for most schema languages.

This is because of their pass/fail or PSVI approaches.  Something is valid or invalid against a schema, rather than having a processing or semantic status assigned to it.

I suppose DTDs and XSD can model "must accept"  by implying an attribute value to elements they know about.  Schematron can let you assign roles to assertions or patterns, typically error, warning, note,  and potentially other properties.

The most commonly used standard way to do this is Microsoft's "secret weapon" for futureproofiing which is the MCE (Markup Compatability and Extensibility) spec. It is part of OOXML but used by them in many other places. There is no equivalent in ODF (I tried to propose adopting MCE but some mix of NIH and the reality of the more limited resources of the ODF developers was against it). ISO is currently rewriting the MCE to be more implementable, I believe.  MS has documentation on how they use it in OOXML at

For MCE,  the approach is to do things by markup rather than schemas. Primarily chunks or information units, not individual elements.  Makes sense.


On Wed, Apr 10, 2013 at 8:06 AM, Simon St.Laurent <simonstl@simonstl.com> wrote:
Press releases are often a better place to find an explanation of what specifications are meant to do than the specifications themselves.  The W3C in particular has had strong press operation for a long time, and generally conveyed its plans for specifications pretty well.

Based on that theory, I've been exploring the archive of schema-related press releases, and found this odd sentence.  The opening is just the usual prior agreement promise, but I'm not sure what to make of the conclusion:

When XML is used to exchange technical information in a multi-vendor environment, schemas will allow software to distinguish data governed by industry-standard and vendor-specific schemas, and help applications know when it is safe to ignore information they do not understand, and when they must not do so.

This sounds more... intricate than validation, but I'm guessing that's all it really is.  Is there something more to "when it is safe to ignore information they do not understand, and when they must not do so"?

That last bit seems to expand to "must not [ignore information they do not understand]".  That fits quite nicely in the approach I'm describing - but not so much with any XML Schema application I've encountered.

Any thoughts?

Simon St.Laurent


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