Dependencies and Their Types

Dependency & Its Types in DBMS:

1. Functional Dependency (FD): This is the most important dependency. An attribute Y has a functional dependency on an attribute X (written as X → Y) if each value of X is associated with exactly one value of Y. For example, `StudentID → StudentName`.
   • Full Functional Dependency: An attribute is fully functionally dependent on a composite key, but not on any subset of that key.
   • Partial Dependency: An attribute depends on only a part of a composite primary key.
   • Transitive Dependency: An indirect dependency where X → Z because X → Y and Y → Z.
2. Multivalued Dependency: This occurs when the presence of one or more rows in a table implies the presence of one or more other rows in that same table. It exists when a table has at least three attributes (e.g., A, B, C), and for each value of A, there is a set of values for B and a set of values for C, where the sets for B and C are independent of each other.
3. Join Dependency: This specifies that a table can be losslessly decomposed into smaller tables and then be reconstructed by joining those smaller tables.