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RE: Are people really using Identity constraints specified in

sch mas de cam

Good summary.  

CAM however is dastardly - in that it allows extensible function calls - to
procedural code blocks - exactly for that backend integration.  Of course both
parties (sender / receiver) may need access to that - but CAM has a web service
pluggable interface - that allows that. Having the declarative world call the
procedural world imposes of course a constrained interaction model - so that
the declarative model is not broken.  Such calls are essential for answer
realworld rule needs like - 'is quantity_ordered =< stock_on_hand' where the
web service call to the ERP warehouse management system can answer this.

Cheers, DW.
Quoting "Roger L. Costello" <costello@m...>:

> Hi Folks,
> An excellent, important discussion!  Below I have summarized what I perceive
> as the key issues.  Comments are very welcome.
> Here are the two problems that we have been considering:
> Problem #1
> A company has employees.  The current company policy is that the minimum age
> of employees is 16.  What happens when a 15 year old whiz kid is hired?
> Validation by the IT department of the data file for this new employee will
> result in sending up error flags.  Should the IT department run the
> business, or should the business run the IT department?
> Problem #2
> A person from the UK makes an online purchase from a US supplier. The online
> supplier requires entry of a two-letter code in the "State" box and a
> numeric value in the "postal code" box, despite the fact that the person
> entered UK as the country. So, the person entered "ZZ" as the state and
> 12345 as the postal code.  Does validation result in forcing people to
> supply incorrect information?
> In discussing these problems, two categories of validation were identified:
> 1. "Syntactical" or "structural" validation 
> 2. "Semantic" or "business rule" validation
> "Syntactical" or "structural" validation is useful in eliminating a certain
> number of mechanical data entry errors, such as leaving out required items
> or putting strings in fields that require numbers (e.g. phone numbers,
> dates, etc.)   
> "Semantic" or "business rule" validation captures some aspect of a business'
> requirements.  An example is validating that a credit card is acceptable.
> There are two categories of tools for doing validation:
> 1. Declarative-based tools
> 2. Procedural-based tools
> The declarative-based tools include XML Schemas, XForms, CAM.  The advantage
> of these tools is that the constraints they express are easily changed.  The
> disadvantage is limited expressiveness (consequently, it may be very
> difficult to express semantic/business rule constraints using these tools).
> The declarative-based tools are typically client-side tools.
> The procedural-based tools include Javascript, Java, C#, etc.  The advantage
> of these tools is that they have rich expressiveness.  The disadvantage is
> that changes are not as easily made.  The procedural-based tools are
> typically back-end tools.
> The declarative-based tools are better suited for "Syntactical" or
> "structural" validation. 
> The procedural-based tools are better suited for "Semantic" or "business
> rule" validation.   
> Other Issues
> In a highly distributed system there is no definable "back-end" where all
> business rules may be validated.   In such a case, it may be beneficial to
> push semantic/business rule validation out to the client-side.
> XML Schemas, XForms, CAM, Javascript - these are all a "means to an end".  
> If you are going to validate, then validate! In Problem #2 the user was
> forced to enter a 2-character state code, despite being from the UK.
> Several people noted that the problem was not with too much validation, but
> with not enough validation.  If the system had been doing a good job
> validating then "ZZ" would not have been allowed for the state code.
> Further, full validation would have determined that if the country code is
> UK then no value is required for the state code.
> /Roger
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