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   RE: [xml-dev] Best Practice - beyond schema

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The problem of a schema that matches multiple customers 
with different requirements is to establish authoritative 
controls.  Multiple authorities are in effect.   

The single schema approach with multiple optional 
elements can govern but is too weak to be said to  
govern transparently.   The problem of multiple schemas is that 
the control is referential beyond the fact of the specific 
schema used for the local or specific transaction, so 
not unified and proof must always be offered that the 
schema-of-use is in fact, mapped correctly to the local 
rules of the process.   This means transparency is lost. If the 
authorities are local, the schema from which 
the schema-of-use is derived is the governing schema and 
the authority of reference has little value beyond being a
library registry.

An alternative is to move the local definition to a transformation 
document, eg, XSLT over the XML Schema.   The technical 
advantage here is to have the modifications in a single 
automated document including any value constraint controls 
which presumably will be local  The XML Schema is one and the authority 
is centralized.  The XSLT modifier is one and is owned by the 
local authority.  

Given the nature of electoral processes, the ability to 
vette the controls and cite them as singletons (one XML 
Schema, one XSLT per local definition) would seem to be 
important to the transparency of the process.


-----Original Message-----
From: Paul Spencer [mailto:paul@alphaxml.com]

There are two reasons for needing to go beyond XML Schema on a project
that is using XML Schema as its base constraint syntax. The first is
where XML Schema cannot express the constraints required, for example,
a section of a message that is required if the value of a previous
element is "yes", but not if it is "no". Languages such as Schematron
go some way to address this and can be used either embedded in an XML
Schema schema or as free-standing documents. I will shortly be making
recommendations in this area to the UK Govt, and would welcome a
discussion here at some point.


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