updated: 2022-01-23_12:32:31-05:00

updated: 2021-11-18_06:25:56-05:00

Trivial Functional Dependency
FD: A1,A2...An -> B1, B2 ... Bm
if B1, B2... $\subseteq$ A1, A2 ... An
then the above FD is called a trivial FD

  • RHS attributes of a trivial FD are a subset of LHS's attributes
  • title,year -> title
  • title -> title

Nontrivial Functional Dependency

A1 ... An -> C1 ... Ck

A1...AnC1...Ck
aaaccc
bbbbb
**###
  • '*' is trivial attributes, '#' is non trivial attributes for b

{AB}$^+$={ABCDE}
trivial:
AB -> AB
nontrivial:
AB -> CDE