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From: Mike Champion [mailto:mc@xegesis.org]
Sent: Monday, May 26, 2003 2:17 PM
Subject: [xml-dev] Testability and Schema validity
...
For example, consider a purchase order format definition. ...
But a real test regime will require constraints that
aren't expressible in any XML schema language AFAIK:
We noted this issue with HTML forms, and added the ability to bind
properties to instance nodesets via XPath expressions. XForms offers a
"constraint" property, which is an XPath expression that must be true in
order for the nodeset to be valid. The constraints on all nodes that are
submitted must be true, and the resulting instance must be valid according
to the Schema, before the form instance is submitted.
The live data constraints you mentioned ("approved by", "currently in
stock", etc) can be retrieved from within XForms while the form is being
filled out, without having to retrieve the entire host document. Data that
is not part of the submitted instance can be sent along with the host
document as additional instances, or pulled in later, or received as a
response to a submission of some other instance.
Finally, XForms allow the declaration of XPath extension functions, so a
client can also offer additional XPath functions that can be used in
constraint expressiona.
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