Estimating size of tuples

can you please explain what you are trying to do

Say r1 (ABC, r2 (CDE) and r3 (EF) with primary keys A C and E. I wanted to estimate the sizes of these tuples if r1 has 1000 r2 has 1500 and r3 has 750?

can ask more :) until somebody else answer your question

what is R1, R2, R3
are those tables? ABC, CDE, EF are columns? A C E are PK on each table?
R1 has 1000 means it has 1000 records (1000 unique A value)?

by tuple what do you mean, can you give samples...

Yes, you are exactly correct on all your assumptions.

Suppose we have
R(a,b) with T(R) = 1000 and V(R,b) = 20
S(b,c) with T(S) = 2000, V(S,b) = 50, and V(S,c) = 100
U(c,d) with T(U) = 5000 and V(U,c) = 500
What is the estimated size of R    S    U?
First join R and S (on attribute b):
estimated size of result, X, is T(R)*T(S)/max(V(R,b),V(S,b)) = 40,000
by containment of value sets, number of values of c in X is the same as in S, namely 100
Then join X with U (on attribute c):
estimated size of result is T(X)*T(U)/max(V(X,c),V(U,c)) = 400,000

I am totally lost :)