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> > These types of constraints tend to fall into the realm of "business
> > rules",
> > and in no way belong in a data schema language
>
> It has been standard practise from the beginning of markup
> languages to accept multiple units of measurement, such as
> inches, pica, cm.
>
> These are hardly "business rules".
I've never see a satisfactory definition of the term "business rules", but in my book, the art of translating from picas to cms is as much part of the typographer's business as the calculation of compound interest is the banker's business and the calculation of longitude is the geographer's.
Uche is right, there is absolutely no rational and logical reason why dates and times, alone among all units of measure, should have found their way into XML Schema while other units have not. They certainly shouldn't have been defined as primitives, with a status that user-defined types can never aspire to. Too much SQL thinking by far.
Michael Kay
Software AG
home: Michael.H.Kay@ntlworld.com
work: Michael.Kay@softwareag.com
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