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Re: [xml-dev] Epischema Article on XML.com

Hi Felix,

I remember your presentation -- 2010 was the first XML Prague conference that I attended!

Whether it's better to write a complete schema for the constrained base vocabulary from scratch, to use other schema customization methods, or to use another layer (Schematron, epischema) is a pragmatic question.

If I need a highly restricted HTML schema, I'll probably write one from scratch, as you did.

If you think of an EPUB editing tool that wants to enforce certain constraints on the use of headings, the content must still be valid against XHTML 1.1 (for EPUB 2) or to a variant of (X)HTML5 (for EPUB 3) in the first place. But you don't want to look into either of the base schemas in order to find out which detailed models need tweaking. If there's a constraint layer that can be added on top of either base schema, you'd certainly prefer this.

Of course there are other customization methods than adding Schematron or epischema on top. But base schemas often don't provide redefinable content models at the desired granularity, or the schema language doesn't offer context-dependent (co-occurrence) constraints at all.


On 01.05.17 09:55, Felix Sasaki wrote:
Hi Gerrit,

I think this approach is very useful. I did something similar to have a special purpose, XHTML based editing and publication workflow for multilingual document creation, see
and the paper at

Using RELAX NG to constraint (X)HTML could fill a gap that there is in the current Web content authoring technology stack.

- Felix

2017-05-01 9:29 GMT+02:00 Imsieke, Gerrit, le-tex <gerrit.imsieke@le-tex.de <mailto:gerrit.imsieke@le-tex.de>>:

Adding a second Relax NG schema in the way you'd add a Schematron
schema is an (in my view) nice approach to constraining a base schema.
It is orthogonal like Schematron: You don't need to know or modify
the building blocks that the base schema provides.
Unlike Schematron rules, the additional Relax NG schema may be used
by XML editors for content completion.
Those of you who listened to this year's XML Prague presentation
[1,2] about adding a Docbook-like grammar to TEI divs already know
the concept. In a recent article on XML.com [3], I've applied this
approach to HTML, using the HTML-first publishing workflow that Dave
Cramer described [4] as an example.
I've called this approach, that to my surprise (and admittedly
modest knowledge) was hitherto unheard of, "epischema" (epi = on top
Please note that I'm not advocating against the use of Schematron;
on the contrary. It's just that there's an alternative way to
express a certain class of constraints (grammatical ones), and this
alternative provides specific, context-dependent content completion
suggestions as a side effect.
Looking forward to receiving your comments.


[3] https://www.xml.com/articles/2017/04/29/epischemas/
https://www.xml.com/articles/2017/02/20/beyond-xml-making-books-html/ <https://www.xml.com/articles/2017/02/20/beyond-xml-making-books-html/>


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