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In the definition, it says minimal key is a minimal set of attributes needed to identify the table. Does the "minimal" part mean "minimal number of attributes" or "cannot be eliminated"?

For example:

  • For a relation R(A, B, C, D, E, F), the closure of A, BC, and DEF are all {A, B, C, D, E, F}.

Are they all minimal keys? Or is only A the minimal key?

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    Your post gives fragments from the middle of solving a problem, but it doesn't contain enough information to say what the CKs ("minimal" superkeys) are. The accepted answer has guessed what situation you would write that in. Now you can guess back about whether they guessed correctly. That is why you should show the steps of doing your homework. PS You mean "identify a row in the table", not "identify a table". Please don't cross-post to multiple sites. – philipxy Nov 29 '18 at 13:34
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They are all minimal keys.

Minimal means there is no proper subset with the same property.

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