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RE: Can XML Schemas do this?


entropy hell


> -----Original Message-----
> From: Eric van der Vlist [mailto:vdv@d...] 
> Sent: Tuesday, January 21, 2003 14:02
> To: Alessandro Triglia
> Cc: 'John Cowan'; 'Jeff Lowery'; 'Bryce K. Nielsen'; 'xml-dev'
> Subject: RE:  Can XML Schemas do this?
> 
> 
> Hi Alessandro,
> 
> > If the order is regarded as a constraint that the schema imposes on 
> > the documents, then the existence of the constraint can be 
> described 
> > as "less entropy" in the message and the absence of the 
> constraint can 
> > be described as "more entropy" in the message.
> 
> That's a nice metaphor.
> 
> > A possible question is, Why do we want to put "more entropy" in the 
> > message if we are not interested in the extra "information" that 
> > corresponds to the increased entropy?  (Or worse, when the extra 
> > "information" is completely undefined and the readers can infer just
> > anything?)
> 
> Because a limited and controled amount entropy is life! Of 
> course, too much entropy is hell, but entropy is what make 
> you feel comfortable, warm and cosy in front of your fireplace... 
> 
> To switch back to computer related subjects, I always feel 
> more comfortable when there is more than one way to do things 
> and when no unecessary constraints are imposed to me.
> 
> Isn't it why XML 1.0 allows so many syntactical variations?


I guess the main distinction is between:

1) the syntactical variations that (most) people perceive as mere
syntactical variations (and therefore are not tempted to attach
semantics to), and 

2) the variations that are likely to mislead people into inferring some
semantics that was not intended.

Examples of (1) are: attribute order, empty-element tags vs. start-tag
end-tag, presence and usage of end-of-line characters, etc.  These
variations are inherent in XML 1.0 and CANNOT be controlled by a schema.
(Other similar variations are inherent in XML Schema and cannot be
controlled by a schema either.)

Examples of (2) are those variations that are really UNDER THE CONTROL
of a schema but that the schema fails to exercise control over (thus
resulting in both lack of constraint and lack of specific semantics ->
"unused" entropy).

Alessandro


> 
> Eric
> -- 
> Curious about Relax NG? My book in progress is waiting for 
> your review!
>                                    
> http://books.xmlschemata.org/relaxng/
> 
> --------------------------------------------------------------
> ----------
> Eric van der Vlist       http://xmlfr.org            
> http://dyomedea.com
> (W3C) XML Schema ISBN:0-596-00252-1 
> http://oreilly.com/catalog/xmlschema
> --------------------------------------------------------------
> ----------
> 
> 


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