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The best example I can think of relates to engineering design criteria.
Any physical capacity or design limit arising from an architecture or its interactions with another system will give rise to ranges which might well be placed within a schema.
One instance: an XML grammar which describes telecom equiptment installations. There are very large numbers of countable parameters: provisionable elements, capacities, etc. I am not quick to dismiss these as business rules. It is a tough job to convince a Test Engineer that a schema language which imposes hundreds of <optional> declarations will result in fewer bugs in the code or in the test cases than one which can do the same thing in a one-liner.
By the way, I like RNG and appreciate the discipline imposed by the current cardinality constraints, so I'm not arguing against it. But I think it would remove a stumbling block that could lead to wider adoption (even if it is just a minor point to some).
Just my (cent,cent+)
Joe English wrote:
> Mike Fitzgerald wrote:
>>Bob Foster wrote:
>>>From: "Mike Fitzgerald"
>>>Also, RELAX NG lacks the precise occurrence restraints of XML
>>>Schema that is, no minOccurs/maxOccurs. RNG supports only the common RE
>>>or DTD constraints ? * + as <optional>, <zeroOrMore>, and <oneOrMore>.
>>>Yes, but that's just shorthand; it doesn't add any additional capability.
>>In some respects, it is shorthand, e.g.:
>>? is <optional> is minOccurs="0" maxOccurs="1"
>>but you can't say a min of 9 occurrences with a max of 12 in RELAX NG; you
>>can in XML Schema with minOccurs="9"/maxOccurs="12". However, M-N
>>constraints are on the official docket for RELAX NG as a separate spec.
> What are the real-world use cases of minOccurs and maxOccurs?
> In my experience, occurrence constraints specifying anything
> other than zero, one, or many are almost always an indication
> of a bad design decision somewhere in the system.
> (Or maybe that *is* the use case? To be able to accurately
> describe badly normalized legacy RDBMSs and other such things?)
> --Joe English
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