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   Re: [xml-dev] Are people really using Identity constraints specifiedin X

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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)


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