A functional dependency is a relationship between or among :

Question

Accepted Answer

The correct option is (4):
A functional dependency (FD) is a fundamental concept in Relational Database Management Systems (RDBMS) that defines a constraint on a set of attributes within a single relation (table). Formally written as A $\rightarrow$ B, it means that the value of attribute set A uniquely determines the value of attribute set B. In simpler terms, if two rows in the table have the same value for A, they must also have the same value for B. Therefore, the relationship is explicitly between one set of **Attributes** (the determinant) and another set of attributes (the dependent), making this the most accurate answer. Functional dependencies are the bedrock for the process of database normalization, ensuring that data redundancy is minimized and data integrity is maximized.

The incorrect option is (1):
Tables are the physical representation of relations in a database. While functional dependencies are enforced within a table, the dependency is not a relationship *between* tables. Relationships *between* tables are typically represented by foreign keys, which link the primary key of one table to a column in another. Functional dependency is a property of the internal structure of a single table, concerning its columns, or attributes.

The incorrect option is (2):
Rows, also known as tuples, contain the actual data instances of the relation. A functional dependency is not a relationship among individual rows; rather, it is a rule or constraint that must hold true for *all* rows in the table simultaneously. The FD rule is checked by comparing the values of attributes across the entire set of rows, ensuring consistency across the data records.

The incorrect option is (3):
A relation is the formal, theoretical term for a table. Although a functional dependency is *defined on* a relation, the dependency itself is an intra-relational constraint that governs the values of its constituent attributes. The functional dependency does not link one entire relation to another relation. If the question were about the entity-relationship model, this answer might be considered, but in the context of functional dependency, the focus is internal to the relation's structure.