xml-dev - Property role and domain (was: Playing with XML Schema & XSLT)

[Kay Michael <Michael.Kay@icl.com>]

> "About that, I regret that the first example in the 
> introduction to XML Schema has a tag <shippingDate> , and not
<shipping><date>, > which is extendible, and allows machine understanding."
>
This need to represent both the role of a property and its domain has always
been a problem in data modelling, for example the concept of domain was in
Codd's original relational model but didn't make it into SQL until much
later, and never made it into the core of the language.
 
For XML I struggled a little to identify best practice on this when writing
Chapter 4 of Wrox Professional XML: the discussion of alternative approaches
is on page 129-130. I came to the conclusion that <Billing><Address> was
probably preferable in theory to <Billing.Address> or <Address
role="Billing"> or <Billing type="Address">, but rather clumsy in practice;
and in the end I dodged making a firm recommendation.

Any other views on this? Does it become easier with XML Schema replacing
DTDs?

Mike Kay 

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