Formal definition of a key
•
A
key
is a set of attributes A
1
, ..., A
n
s.t. for
any other attribute B, A
1
, ..., A
n
à
B
•
•
A
minimal key
is a set of attributes which
is a key and for which no subset is a key
•
•
Note: book calls them
superkey
and
key