DBMS
Functional Dependencies Explained
A functional dependency says that whenever two tuples agree on X they must also agree on Y. It is a rule about every possible instance, not an observa...
Functional Dependencies
Functional dependencies, attribute closure, Armstrong axioms, minimal cover and finding candidate keys.
5 notes
Notes
DBMS
Attribute Closure, Step by Step
The closure of an attribute set is everything it determines. Computing it is a short mechanical loop, and it is the single tool used to find keys, tes...
DBMS
Armstrong Axioms and Inference Rules
Three primary axioms - reflexivity, augmentation and transitivity - are sound and complete, meaning they derive every dependency that follows and none...
DBMS
Finding All Candidate Keys of a Relation
A reliable method for finding every candidate key: classify attributes by where they appear in the dependencies, build a compulsory core, then extend...
DBMS
Equivalence of FD Sets and Minimal Cover
Two dependency sets are equivalent when each implies the other. A minimal cover is the smallest equivalent set, computed in three steps, and it is wha...