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Q: 

DTD syntax for SQL UNIQUE constraint

Hi,

I am moving from accessing data from database to xml for my application specific need. I am currently writing DTD for the xml by referring to my sql table schema. I have defined a constraint on 4 columns to be unique(These 4 columns defines a directory structure 3 step deep so together they have to be unique eg. dir1/dir2/dir3/dirA and dir1/dir2/dir3/dirB). I know I can use ID to maintain uniqueness of an attribute. How can I define this for 4 attributes together.

Thanks,

Shripad

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