Functional Dependencies
•Definition:    A1, ..., Am à B1, ..., Bn holds in R if:
•
•"t, t’ Î R, (t.A1=t’.A1 Ù ... Ù t.Am=t’.Am Þ t.B1=t’.B1 Ù ... Ù t.Bm=t’.Bm )
•
Bm
...
B1
Am
...
A1


if t, t’ agree here


then t, t’ agree here
t
t’
R