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Howard Katz wrote:
Jonathan's chapter provides a great introductory overview of XQuery
features. Don Chamberlin's excellent chapter on "Influences on the Design of
XQuery" can also be found online at

     http://www.informit.com/content/downloads/chap2_0321180607.pdf
This is very interesting chapter.  Quotes I found interesting:

"XML Schema was designed to support the validation of documents
rather than to serve as the type system for a query language." 

Oh dear. What about Usage Scenario 5 of the XML Schemas Requirements[1]?
    "Use schema to help query formulation and optimization.

    A query interface inspect XML schemas to guide a user in the formulation of queries.
    Any given database can emit a schema of itself to inform other systems what counts as
   legitimate and useful queries."

And the design requirement that the datatypes must "define a type system that is adequate
for import/export from database systems (e.g., relational, object, OLAP)" 


Other good quote, showing the false economy of non-modularity in big specs:

* XQuery's design influenced by XML Schema's provision of
  "a set of primitive types, a type-definition facility, and an inheritance mechanism...
   (and) the validation process... Nevertheless, members of the working group
   attempted to modularize the parts of the language that are related to type
   definition and validation, so that XQuery could potentially be used with
   an alternative schema language at some future time."


Cheers
Rick Jelliffe


[1] http://www.w3.org/TR/NOTE-xml-schema-req
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