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Re: [xml-dev] Need a language whiz: An XML Schema "specifies" howdata is to be structured? "describes"? "constrains"?

On 08/01/2018 11:14, Tony Graham wrote:
On 08/01/2018 09:20, Rick Jelliffe wrote:
I still don't see what the novelty of "epischemas" is supposed to be,
 apart from giving a name (which is welcome).   James Clark did this
 parallel grammar technique for HTML IIRC, as a way to reconstruct
I don’t want to boast about it, but I consider naming this thing quite a feat. As the jokes go, naming things is one of the hardest problems in computer science after all!

IIRC, Gerrit did refer to James Clark's precedent (and its absence of a
name) in his talk, though I can't find a mention of it in either of
Gerrit's slides or paper.
We’d have to watch the full, excruciating video in order to find that out. I don’t remember either.

What I did mention in the paper is that epischemas might resemble architectural forms (whose name, btw, is quite pretentious, given their relatively minor merit in computer science ;-) superficially, but actually epischemas (local constraints for elements with the same name) are the inverse of architectural forms (different element names reduced to a common grammar).

exclusion exceptions (i.e. that an <a> could not contain an <a> etc)
 without combinatorial explosion.  Schematron supported multiple
patterns in parallel from the start.   DSDL's NVRL was based on
selecting different sections of documents and running them through
different schemas (including in parallel).  Lloyds of London
Financial Markets use of layers of increasing complexity (IIRC a
basic grammar, then a complex grammar, then a Schematron) to weed out
bad transactions efficiently was widely reported.  And the idea of a
Bloom filter is basic CS knowledge.
Everybody here is pro-Schematron, but Gerrit's stated reason for using
multiple schema bundled with NVDL is context-aware content completion in
The other reason was that some problems, such as modeling the permitted TEI div types after DocBook’s part/chaper/section elements, are more naturally specified as a grammar than as Schematron rules. Not all XML grammar languages qualify for modeling it though. You need an anything pattern that allows exclusions. These are available in Relax NG and XSD 1.1.

I’m a pro-Schematron guy, btw.


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