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

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while i already have a stated position on the dangers of overly strict 
checking systems - i like to see easy to spot errors so i can get a 
measure of how many hard to see errors are in the system - i do think 
there is a very important and valid role for it systems to implement and 
enforce business rules.

while this is not necessarily the same as constraint checking - indeed 
it can be much more complex - it is something that makes our systems 
more than just data/document repositories and number crunchers.

i have any number of examples of where there has been a supposed system 
failure, only to find on investigation it has been a breaking of the 
business rules and the it system is the warning system to management 
that something needs to be investigated.


Bullard, Claude L (Len) wrote:

>Michael is right, but this isn't a one size fits all decision. 
>Loose filters allow dirt to seep into the system.  The architectural 
>question is what are the right places to put such rules into 
>a system?  We are aware of different technologies for this, 
>and it is a good thread to out the issues if that interests 
>the members of this list.
>That a technology can accomplish a task doesn't mean it 
>is the right tech for that task.  It doesn't mean it isn't. 
>I suspect this is another task situatedness issue, but given 
>a services architecture, one might want to inquire about 
>tasks relative to their roles in distributed processes 
>that are candidates for orchestration.
>From: Roger L. Costello [mailto:costello@mitre.org]
>Michael Kay wrote:
>>I tend to be a little wary of constraints myself. 
>>Many of those you see in student textbooks are 
>>misguided. If I see a schema (XML or RDB) with the
>>constraint that employees must be over 16, I ask 
>>myself what the IT department would do if the 
>>business decided to hire someone under 16. If
>>there's a rule that an employee's manager must 
>>themselves be an employee, I ask what would 
>>happen when someone is told that they now report 
>>to a contractor. 
>This is excellent:
>>It's not the job of computers to limit what people 
>>are allowed to do (or the job of the IT department 
>>to regulate the business). 
>The following innocuous sentence has profound implications  
>on the role of schemas:
>>A guideline I use is that constraints should be there 
>>only to protect the IT system itself from data that 
>>it cannot handle.
>Would you elaborate upon this sentence Michael?  I believe
>that you are saying that the role of a schema is to define
>things such as:
>- ensure that a "date" is indeed a valid date
>- ensure that an "age" is indeed a valid age
>The role of a schema is not, for example, to specify:
>- the "age" must be at least 16.
>So, your guideline says: use schemas to specify datatypes
>for objects, not their range of values.  Is that a fair
>summary of your guideline?  /Roger
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fn:Rick  Marshall
tel;cell:+61 411 287 530


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