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RE: Principle of Least Power (was Re: Agenda of 7 February 2006 T AG teleconference)

From: Bullard, Claude L (Len) <len.bullard@intergraph.com>
Date: Wed, 8 Feb 2006 08:39:19 -0600
Message-ID: <15725CF6AFE2F34DB8A5B4770B7334EE0BB1FE45@hq1.ingr-corp.com>
To: 'Dan Connolly' <connolly@w3.org>, Elliotte Harold <elharo@metalab.unc.edu>
Cc: "'Henry S. Thompson'" <ht@inf.ed.ac.uk>, noah_mendelsohn@us.ibm.com, Vincent.Quint@inrialpes.fr, www-tag@w3.org

Schematron can express co-occurrence constraints.  DTDs can't.

It is more expressive.  The trick is to know if that is something 
you want to express and should you use it.  Metrics of power. To 
know that, one has to understand the difference of power between 
a declarative approach based on paths and one based on a hierarchy 
or named structures in a BNF analog.  Both are used to express schemas 
but are not equally powerful.  One could compare xsd and some of its 
antecedents for an apples to apples comparison but that doesn't really 
make the point.  For example, the Microsoft submission for xsd was 
quite a bit less powerful but the W3C selected xsd.  Did the W3C 
violate the principle or is the principle not a design criteria?

len


From: Dan Connolly [mailto:connolly@w3.org]
Sent: Wednesday, February 08, 2006 8:30 AM

I suspect it's still more expressive than DTDs, though I'm not certain.
Surely the XPath string and numeric operations are more expressive
than DTDs. Seems like an interesting research topic.
Received on Wednesday, 8 February 2006 14:39:29 GMT

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