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

[johns@syscore.com (John F. Schlesinger)]

Mike Kay wrote:
"This need to represent both the role of a property and its domain has
always
been a problem in data modeling, 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."

I think we can exaggerate the extent to which designing XML messages and
documents is data modeling. An XML message from one business object to
another is more like a view than a table - that is, it represents one
application's view of, perhaps, a large number of tables. The mark up should
reflect that view and say as much as possible about what the application
means by the information it is sending or receiving. That is why I don't
like elements called <Address>, <Date>, <Name> or <Phone>. If you replace
them with <WhereToBill>, <WhenToBill>, <WhoToBill> and <AssistantPhone> you
are pinning down much better what you mean by the elements.

Yours,
John F Schlesinger
SysCore Solutions
212 619 5200 x 219
917 886 5895 Mobile

-----Original Message-----
From: Kay Michael [mailto:Michael.Kay@icl.com]
Sent: Thursday, July 06, 2000 5:35 AM
To: 'johns@syscore.com'; 'Jean-Marc Vanel'; xml-dev@xml.org;
wwbota@egroups.com; daniel.rivers-moore@rivcom.com;
Ioana.Manolescu@inria.fr
Subject: Property role and domain (was: Playing with XML Schema & XSLT)


> "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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