FD (Functional Dependency)

A Functional Dependency (FD) in a database is a relationship where the value of one set of data determines the value of another set. For example, if knowing a person's Social Security Number always reveals their full name, then the Social Security Number functionally determines the name. This concept helps ensure data is organized efficiently, avoiding duplication and inconsistency. Essentially, FDs define rules about how data relates within a database, ensuring that certain pieces of data can predict or dictate other pieces, which maintains the integrity and correctness of the stored information.