Wednesday, January 21, 2004

Xpath business rules rule 

via Daniel Cazzulino Business Rules, OCL, XML and Schemas DonXML is proposing extensions to OCL to express business rules that can be used at code-gen time and at run-time.
He mentions my Schematron implementation called Schematron.NET, which allows many business rules to be expressed simply in terms of standard XPath expressions. I believe such an XPath-based language is good enough to express almost every business rule.

Udi Dahan commented as an example, a rule "only a bank manager can authorize a loan above X" which he said couldn't be expressed with Don's idea. It could, indeed, with something along these lines (XPath-like):

<assert test="sec:principal-role('BankManager') and po:Loan/@Amount < 1000">
  Only a BankManager can place a loan of more than $1000.

Note that XPath extensibility allows for more domain-specific extensions to be active, which can even check against databases, etc. For example, something like this:

<assert test="crm:customer-id(po:CustomerId)" />

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