DBMS
Lossless Decomposition and Dependency Preservation
A decomposition is lossless when joining the pieces reproduces the original exactly, and dependency preserving when every dependency can still be chec...
#Functional Dependency
Dependencies, closure and Armstrong axioms.
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DBMS
BCNF and BCNF Decomposition
BCNF requires every determinant to be a super key. It is stricter than 3NF, removes the last key based redundancy, and sometimes cannot be reached wit...
DBMS
Third Normal Form and Transitive Dependency
A relation is in 3NF when it is in 2NF and no non prime attribute depends on another non prime attribute. It is the practical target for most producti...
DBMS
Second Normal Form and Partial Dependency
A relation is in 2NF when it is in 1NF and no non prime attribute depends on only part of a candidate key. It only ever matters when the key is compos...
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...
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
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
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
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...