Terms

• Candidate Key: A minimal set of attributes that uniquely identifies every tuple in a relation.

• Superkey: Any set of attributes that uniquely identifies tuples (a candidate key is a minimal superkey).

• Prime Attribute: An attribute that is part of any candidate key.

• Functional Dependency (X → Y): For any two tuples with the same X values, the Y values must also be the same.

• Trivial Functional Dependency: X → Y where Y ⊆ X (always holds).

• Minimal Cover: A reduced set of functional dependencies F equivalent to a given set E (F⁺ = E⁺), such that:

  • Every right-hand side is a single attribute

  • No dependency can be removed without changing the closure

  • No attribute can be removed from any left-hand side without changing the closure

• Primary Index: An index on the ordering key of a sorted file (typically sparse).

• Secondary Index: An index on a non-ordering field (always dense).

• Sparse Index: One index entry per disk block.

• Dense Index: One index entry per record.