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Re: [xml-dev] Is Schematron (using XPath 2.0) functionally a superset of XML Schemas?

> There tends to be a tradeoff between using languages that are more
> powerful or expressive vs. being able to figure out easily what's being
> said.

I has been notoriously difficult for people to figure out what's being
said with many different variations of XML Schema, and thereby to
produce tools that can figure out what is being said. I suppose this
is something to do with how the standard is written but nonetheless I
believe the world we live in is one in which XSD is not a good example
of least power leading to more comprehensibility.

>So, whatever its other pros and cons, it's pretty simple at the XSD
> component level to express that element E has a type T that allows just a
> sequence (A,B,C).

It is pretty easy, dependent on how you do it.

> For the record, The Rule of Least Power Finding [1] raises these issues
> primarily in the context of resource representations on the Web, for which
> it's almost always good to use the weakest language that will do:  if your
> Web data is declarative (HTML, XML, etc.) then tools like Google spiders
> can grok it to find the text, the links, etc.; if it's imperative or
> Turing complete (think Flash .swf files), then that's hard.  I'm not
> making the case that for schemas the weaker language is in general better,
> just that it's a tradeoff.

the tools, google spiders and what not, can currently grok XML
Schemas, Schematron, and most other variations of XML at the same
level of grokability.

That said for bots analysing understanding Schematron, Schemas, XSL-Ts
it is probably not important to know everything it does, it is just
necessary to be able to tell you certain things about it which can be

what namespaces do they handle as input namespaces
for xsl-t what namespaces are their output namespaces
version of the instance
search in text nodes

there are things that XML Schema would allow you to do easier with a
bot such as return all schemas with elements A,B,C in namespace X. But
I believe this is still reasonably possible in Schematron and XSL-T.
There are of course search requirements for the Schematron and XSL-T
that are not found in XML Schema.

Bryan Rasmussen

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