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Home -> Community -> Usenet -> comp.databases.theory -> Two definitions for functional dependency.
Given a relation R(x,y) when does x->y functional dependency holds?
Let's try several relational algebra expressions over R.
2a. R(x,y') /\ R(x,y"). Let's join it with the relation y'!=y". The x-
>y holds iff the resulting relation is empty. This cute formulation
has been already discussed on this forum. What is new (at least for
me), is the option 2b:
2b. R(x',y) /\ R(x",y). Let's project this relation to <x',x">. The x->y holds iff the resulting relation is an equivalence relation. Received on Thu Mar 29 2007 - 15:56:27 CDT