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RE: [xml-dev] Separate data from rules ... is the XML Schema 1.1 <assert> element a step backwards?

Regarding where to put the checking:

1. User Experience is always better if you let the user know immediately
when they have broken a rule.  So this requires a check to the rules engine
and then a properly crafted User Experience response - like a good message
and perhaps a pointer to some help.  All this can be localized.

2. Your business logic level should reject invalid where your Business logic
API does not explicitly enforce rules.

3. The database can have "structural" rules but the error messages may leave
something to be desired and may not be localizable.

-----Original Message-----
From: Andrew Welch [mailto:andrew.j.welch@gmail.com] 
Sent: Wednesday, June 17, 2009 6:13 AM
To: Michael Kay
Cc: Costello, Roger L.; xml-dev@lists.xml.org
Subject: Re: [xml-dev] Separate data from rules ... is the XML Schema 1.1
<assert> element a step backwards?

>> First an example of a business rule:
>>     A Level 1 manager has a maximum signature
>>     authority of $10K.
>>     An auto loan applicant, living in Ohio, is
>>     underage if he/she is under 18 years of age.
>>     If a customer has no outstanding invoices,
>>     then the customer is of preferred status.
> I agree those are business rules and are best kept out of a schema.
> What's more difficult are rules like "Every branch of the bank has a
> manager" - that's on the borderline between structural rules and business
> rules.

I've often wondered where you draw the line - do you check everything
possible in the xsd, or only in the application, or both.

There doesn't seem to be a simple answer, but a rough guide is: if you
don't want "branch manager" to ever be null, check it in the schema.
If however, you want a nice error message instead of one mentioning
"invalid content" and "complex type" then let it through to the app.

Andrew Welch
Kernow: http://kernowforsaxon.sf.net/


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