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RE: Are people really using Identity constraints specified in

• To: "Thomas B. Passin" <tpassin@c...>, <xml-dev@l...>
• Subject: RE: Are people really using Identity constraints specified in XML schema?
• From: "Cox, Bruce" <Bruce.Cox@U...>
• Date: Fri, 20 Aug 2004 14:26:57 -0400
• Thread-index: AcSG40ZzgV+etDOuQGGM0Fy6JsXZJA==
• Thread-topic: Are people really using Identity constraints specified in XML schema?

In my world, attorneys speak "business rules" and IT folk speak "data
constraints".  Often, their intention and extension are identical.  A
really good schema is the membrane where these two sets touch each
other, that is, it is equally successful from both points of view.


Bruce B. Cox
SA4XMLT
+1-703-306-2606

-----Original Message-----
From: Thomas B. Passin [mailto:tpassin@c...] 
Sent: Thursday, August 19, 2004 4:59 PM
To: xml-dev@l...
Subject: Re:  Are people really using Identity constraints
specified in XML schema?

Roger L. Costello wrote:

> - The value of the <minimum-age> must be an integer.  This is a 
> constraint on the data.  It will not change over time.

Ha! What happens when the government decides that some relevant age is
67.5 years instead of 67?

> Therefore, an XML Schema should simply constrain <minimum-age> to be 
> an integer.  Higher level applications should implement the business 
> rule that <minimum-age> be further constrained to 16.
> 
> How would you characterize the distinction between "business rules" 
> and "constraints on data"?

A tricky, tricky issue - what is or is not a "business rule".  I suspect
that in practice most constraints that are not business rules are in
place for supposed programming reasons, or by force of habit.

In one project I work on, we have a data type that is a union of 1) an
enumeration of strings, 2) a string that follows a certain regex
pattern, and 3) an integer constrained to a certain range.  No, don't
bother to ask - it's one of those multi-agency reconciliations.

--
Thomas B. Passin
Explorer's Guide to the Semantic Web (Manning Books)
http://www.manning.com/catalog/view.php?book=passin

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