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Re: Are we losing out because of grammars?

> > Looks like we are going towards 4 different types of XML "schema"
> > languages to define:
> >
> > - The structure
> > - The datatypes
> > - The rules
> > - The semantic.
> This is very interesting - I wonder if we might be heading for another split
> such as the one that saw XSL split into T and FO? The differences are
> becoming more pronounced, and the term "schema language" is starting to lack
> definition as a result.
> Eric (or anyone else), how do you differentiate between rules and semantics?

Anyone Else here.

I think the term "rules" needs be clarified.  There are of course what are
sometimes called "business rules", which lie arguably at the semantic
layer.  However, I think Eric means structural rules, which I'd also term
structural constrants.  These do exist at the synctactic level.

I would probably re-state Eric's first and third entries as "structural
patterns" and "structural rules".  The subtle difference is that the
former uses a pattern language and the processing is the binary result of
matching the source against these patterns.  The latter evaluates
generalized expressions against the source, whose results trigger
actions.  One possible set of actions is to accept or reject the source
as valid.

To pick a whimsical analogy, structural patterns are like AI by machine
vision, where the bacterium is identified from the microscope image.
Structural rules are like AI by expert system (Mycin?), which determines
the disease by applying a series of rules, some of which have the action
of narrowing the diagnosis.

It looks as if my version of Eric's suspect line-up is as follows:

 - Structural patterns - DTD, TREX, RELAX, XSchema content model
 - Datatypes - XSchema data types, UML/XMI
 - Structural rules - Schematron
 - Semantics - RDF(S)?, XMI?, UREP?, eCo?

Note all the question marks in the last entry.

Uche's Apothegm: Any combination of S-words("schema" and "semantic"
in this case) results in instant and mutual annihilation with question
marks as the only surviving byproduct.


Uche Ogbuji                               Principal Consultant
uche.ogbuji@fourthought.com               +1 303 583 9900 x 101
Fourthought, Inc.                         http://Fourthought.com
4735 East Walnut St, Ste. C, Boulder, CO 80301-2537, USA
Software-engineering, knowledge-management, XML, CORBA, Linux, Python