Normalization Theory Flashcards
Decomposition is lossless when…
R1 ⋂ R2 -> R1 or R1 ⋂ R2 -> R2
Decomposition is lossy when…
it is not lossless
Functional dependencies
{set of attributes} -> {set of attributes} where th left side uniquely determines the right side
trivial functional dependencies
if the right side contains the left side, the dependency is trivial
closure (F+)
the set of all functional dependencies logically implied by F
closure of attribute sets (a+)
given a set of attributes a, define the closure of a under F (denoted by a+) as the set of attributes that are functionally determined by a under F
superkey
a set of attributes that uniquely identifies each tuple in a relation; if a+ contains all attributes of R, a is a superkey
candidate key
a superkey that cannot be reduced by removing an attribute
dependency preservation
a decomposition is dependency preserving if (F1 ⋃ F2 ⋃ … ⋃ Fn)+ = F+
reflexivity rule
if b ⊆ a, then a -> b
augmentation rule
if a -> b, then ca -> cb
transivity rule
if a -> b and b -> c, then a -> c
union rule
if a -> b holds and a -> c holds, a -> bc holds
decomposition rule
if a -> bc holds, then a -> b holds and a -> c holds
pseudotransitivity rule
if a -> b holds and bc -> d, then ac -> d holds
