Relational Database Design and Modeling for Software Engineers
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Closure of Attribute Sets

You have a table and a list of dependencies. Two questions keep coming up, and both are easy to get wrong by eye.

Is {Student_ID, Course_ID} really a key, or did I miss a column it fails to determine? Does Course_ID -> Dept follow from the rules I was given, or am I assuming it?

Attribute closure answers both, mechanically, with a short loop you can run on paper.

The definition

The closure of a set of attributes X, written X+, is every attribute that X determines. That includes attributes it reaches through a chain of the dependencies you were given.

`X

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