Re: [xml-dev] Key constraint on optional attribute

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Paul Popiel writes:

> is there anyway of placing a key constraint on an optional attribute?

That's what 'unique' constraints are for -- not required to be
present, but required to be unique _when_ present.

If that's not what you meant, more details of your document type and
requirements are needed. . .

ht
- -- 
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
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