What defines a relationship between two attributes indicating that for each unique attribute A, there is only one value of attribute B?

The concept of functional dependency is crucial in understanding relationships between attributes within a database. Functional dependency asserts that if you have two attributes, A and B, then A functionally determines B if each unique value of A corresponds to exactly one value of B. This means that knowing the value of A allows you to uniquely identify the value of B.

In practical terms, if attribute A is a key attribute, then attribute B is dependent on A. For example, if A represents a unique student ID and B represents a student's name, each student ID (A) will always map to one specific name (B). This strict correlation is the essence of functional dependency, making it foundational for database design, especially when organizing data into tables and ensuring data integrity.

The other concepts mentioned serve different purposes and do not encapsulate this specific relationship. Partial functional dependency refers to a scenario in which a non-key attribute is dependent on part of a composite key rather than the entire key. Null indicates the absence of a value and does not describe relationships between attributes. Normal form pertains to the structure of database tables and procedural guidelines to reduce redundancy while maintaining data integrity but does not specifically define the dependency of one attribute on another. Thus, the identification of functional dependency is central to understanding