FW: [xml-dev] Fallacies of Validation ... RE: [xml-dev] Are people really using Identity constraints specified in XML schema?

["Roger L. Costello" <costello@mitre.org>]

I am forwarding an excellent message from Mary Holstege:

-----Original Message-----
From: Mary Holstege [mailto:holstege@mathling.com] 
Sent: Wednesday, August 25, 2004 9:44 AM
To: Roger L. Costello
Subject: Re: [xml-dev] Fallacies of Validation ... RE: [xml-dev] Are people
really using Identity constraints specified in XML schema?


Roger L. Costello writes:
> It would be very useful if we could have a simple example that shows how
> several schemas might be employed, rather than a single schema.  Could
> someone provide an example?  

Here's a really quick example: support all you care about in some phase of
processing is picking up the IDs in a document. Then you define a minimal
schema where everything is open with the appropriate ID attributes. Maybe
you're going to generate an index. In another phase of processing all you
care
about is checking that dates are in the right date range. So you have
another
minimal schema that only pays attention to dates. Or to take another
example,
you have a broad dispatch schema that really just wants to figure out
whether
you have a foo or a bar, but everything else is left loose, because once you
dispatch to the foo-branch or the bar-branch you can put in place a tight
schema that will help you clean your data.

Alternatively, you let go of what I consider the number one schema fallacy:

* validation is a pass/fail operation
Not so, although lots of people are still stuck in that way of thinking,
including, alas, a lot of the vendors.

The schema design goes to great pains to make it possible to do things like
this, for example:
* validate a document against a tight schema, and then ask questions of the
result such as "show me all the item counts that failed validation because
they
were too high"

That is why there is the PSVI, that is why UPA is so important (how do I
know
which item count failed validation if I can't figure out which element
matched
which particle? or failed to match?)

//Mary

btw: xml-dev is a read-only medium for me at the moment, which is why I am
responding privately.