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Re: [xml-dev] Victory has been declared in the schema wars ...

On Nov 28, 2006, at 14:21, David Carlisle wrote:

> Of course this rng based xhtml2 hasn't proved to be overwhelmingly,
> popular, before declaring victory we'd better keep an eye on html5  
> which
> manages to do without dtd or xsd or rng, or any other recognised  
> schema
> language at all.....

I think not having a normative schema for HTML5 is a very good idea.  
None of the current schema languages (not even Schematron) are  
adequate for expressing all the conformance requirements of HTML5.  
Experience has shown that people become too schema-focused if there  
is a normative schema: DTDs aren't adequate for expressing the  
conformance requirements of HTML 4.01, but still people behave as  
though they had checked for conformance when they have validated  
against a DTD.

Still, HTML5 can be counted as a bullet point in favor of the RELAX  
NG camp. The only schema for HTML5 in the works is a RELAX NG  
(Compact Syntax) schema with companion Schematron assertions ( http:// 
syntax.whattf.org/ ). A conformance checker for HTML5 requires non- 
schema checking code to fill the gaps that RELAX NG and Schematron  
can't fill (conveniently or at all). For example, http:// 
hsivonen.iki.fi/validator/html5/ checks for table cell overlap in  
Java code--not in RNG, XSD or Schematron.

But back to RNG vs. XSD:
Dare Obasanjo pointed out an important issue on his blog at
Validation and data binding are different problems.

RELAX NG is great for validation. For this purpose, allowing  
ambiguous grammars and making datatypes just check whether a string  
belongs in a formal language are great features. Trying to introduce  
something as innocent-looking as the RNG DTD compat features already  
becomes an annoyance that gets in the way of writing nice ambiguous  
schemas. Infoset augmentation as a side effect of validation is not  

A lot of people use XSD for data binding. RNG doesn't do data binding  
*by design*, so telling those people to use RNG for data binding  
doesn't seem to help. Personally, though, I have serious doubts about  
whether automated data binding is a good idea--in particular due to  
service versioning concerns. And I am not suggesting that XSD is a  
good solution for data binding, either.

P.S. Readers of this thread may be interested in an online RNG and  
Schematron 1.5 validator:

Henri Sivonen

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