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   Re: [xml-dev] Are people really using Identity constraints specified in

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If I am in charge of managing the applications for this company, I would
rather make a change to a schema than to have to open up source, modify
variables, and then recompile just to enforce an age of 18, say, instead of

I can make this change in one place (the XSD), and the next XML document
that comes in gets the new enforcement rule... seems like, from a developer
point of view, you would want to do as much as possible in the schema,
leaving the complex logic to the application (like we only process sub-par
loans on the third Wednesday of the month) that cannot easily be done in


----- Original Message ----- 
From: "Roger L. Costello" <costello@mitre.org>
To: <xml-dev@lists.xml.org>
Sent: Thursday, August 19, 2004 10:15 AM
Subject: RE: [xml-dev] Are people really using Identity constraints
specified in XML schema?

> Hi Folks,
> Here are some thoughts:
> 1. Constraints on data are not equal to business rules.
> 2. Business rules change.  Constraints on data do not.
> 3. Constraints on data should be specified in XML Schemas.  Business rules
> should not.  Business rules should be specified in higher level
> code.
> Example:
> A company has employees.  The current company policy on the minimum age
> requirement is 16.  Should the company create an XML Schema that
> <minimum-age> to 16?  Or, should the company create an XML Schema that
> simply constrains <minimum-age> to an integer, and let applications higher
> up provide further constraints?
> Answers:
> - Mandating that the minimum age of an employee be 16 is a business rule.
> It is highly likely to change over time.
> - The value of the <minimum-age> must be an integer.  This is a constraint
> on the data.  It will not change over time.
> Therefore, an XML Schema should simply constrain <minimum-age> to be an
> integer.  Higher level applications should implement the business rule
> <minimum-age> be further constrained to 16.
> Comments?
> How would you characterize the distinction between "business rules" and
> "constraints on data"?  /Roger
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