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RE: [xml-dev] XML Schema 1.1 Best Practice: Expressing BusinessRules - Co-Locate or Separate?

Thanks Michael and George.

Michael has challenged us to define the term "business rule". I'll take a go at defining it:

    A business rule is a local constraint.
For example, consider this XML document containing credit card data:

        <issuer>American Express</issuer>
        <number>1234 5678 1234 5678</number>

A community of businesses has agreed to use that markup and that structure. Also, the community has agreed to this set of values for issuer:

    - American Express
    - Visa
    - MasterCard
    - Diners Club

However, each business has its own local constraints on what credit cards it accepts. Business A accepts (American Express, Visa, and MasterCard), whereas business B only accepts (Diners Club).  Thus, each business would like to impose additional, local constraints on top of the community's structure and content data rules.

The set of credit cards that a particular business accepts is a business rule.

    A business rule is local, additional layers of constraints on top 
    of a community's structure and content data rules.

Do you agree with this definition of "business rule"?

Perhaps stating the issue in terms of business rules is too narrowly focused? Perhaps the issue should be broadened to:

   Given a common, community-accepted XML Schema, how should 
   member-specific/local constraints be expressed?

Is that a better issue? 

George points out the benefits of using Schematron for expressing business rules (i.e., local constraints). Does XML Schema 1.1 have a role in expressing local constraints?


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