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   Re: [xml-dev] modeling, validating and documenting an xml grammar

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From: "Chiusano Joseph" <chiusano_joseph@bah.com>

> <Quote>
> 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.
> </Quote>
> Off the top of my head: A student can enroll in no more than X courses
> per semester - so the occurrences of Course information for a student
> would be limited to X occurrences.
Also, there is a difference between trying to specify a structure for declarative
purposes and for validation purposes.  For validation, there is no need for {M,N}.
For declaration (e.g. for use in documentation or to allow easy translation to
arrays or some other implementation format) then {M,N} may be more useful.

However, {M,N} is only one of a zillion kinds of semanticesque constraints that
people have. 

Richard Tobin wrote:
> Mike F wrote
> > This ia not much of a deficiency, such constraints are rare and rarely
> > useful.  Though I did once get a bug report for XSV because it did not
> > accept maxOccurs="4294967296".

> Have to agree that it's not a big deficiency. 

Also, it is probably wrong-headed, if it supposes that schemas act to
determine or checkthe capacity of a system. Having maxOccurs="4294967296" 
will not guarantee that your system will support 4294967296 occurrences.
(SGML allowed a matching of document quantitie with system capacity,
but I don't know whether it was actually much use.)



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