Simon_L (8/14/2008)
but to describe publisher city as functionally dependant on publisher I just cant get...if something is functionally dependant it can be uniquely determined by another attribute. But a publisher_city cant be said to be uniquely identified by a publisher..
If you remember from math class "a is functionally dependent on b" means that you can construct a function A so that for any b there exists exactly one a such that:
a = A(b)
Thus, b determines a, or if you know b then you can determine what a is. Translating this to your city example:
publisher_city = PUBLISHERS(Publisher_name).City
Putting this in SQL/relational terms just means that you can construct a PUBLISHERS table with Publisher_name as the primary key and City as one of the data columns. Or "each publisher is uniquely determined by its name" and "each publisher has exactly one publisher_city".
Hope this helps.
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