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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)