Re: [xml-dev] RELAX NG

[Mike Champion <mc@xegesis.org>]

2/2/2002 3:03:05 AM, tariq abdur-rahim <ecliptoid330@yahoo.com> 
wrote:


>Can anyone briefly explain to me what exactly is RELAX
>NG, how it is implemented, and what is its
>relationship to XML.

RELAX NG is a schema definition language for XML, analogous to W3C 
Schema Definition Language (part 1, structures) but considerably 
simpler and more formally elegant.  It *is* XML in its basic syntax 
(although there is a non-XML "shorthand" syntax for convenient 
editing) and defines the criteria for a valid XML document.  See 
http://www.oasis-open.org/committees/relax-ng/

It is *not* from the World Wide Web Consortium, however.  It is an 
"open standard" in that it is the product of an OASIS technical 
committee operating under OASIS open standards process 
http://www.oasis-open.org/committees/process.shtml. It is being 
incorporated into the "real" international standard ISO 19757
http://www.y12.doe.gov/sgml/sc34/document/0275.htm. 

There are several implementations of schema validators and data 
binding tools that use RELAX NG syntax; these are described in a 
section on on the OASIS relax-ng page mentioned above.  Perhaps most 
significant is Sun's Multi Schema Validator, which handles several 
XML schema syntaxes.  In short, RELAX is as much of a "real" standard 
and viable option for "real" work as is the W3C schema spec.  The 
question of which is most appropriate for a given task is an 
interesting question; see Eric van der Vlist's excellent articles on 
this subject: http://www.xml.com/pub/a/2002/01/23/relaxng.html
http://www.xml.com/pub/a/2001/12/12/schemacompare.html and the ones 
linked off them.

I'm not sure if this is what you were asking with "how is it 
implemented" but as I understand it the elegant mathematical 
underpinnings of RELAX NG make it relatively straightforward to write 
a validator.  See http://www.xml.gr.jp/relax/divideAndValidate.html