Functional dependency scope: A functional dependency (FD) is a relationship between or among which elements of a relation?

Introduction / Context:
Functional dependencies formalize how one set of attributes determines another, guiding normalization to remove redundancy and anomalies.

Given Data / Assumptions:

• An FD is typically written X → Y.
• X and Y are sets of attributes from the same relation schema.
• We assume classical relational theory.

Concept / Approach:
An FD states that, for any two rows, if the X attributes match, then the Y attributes must also match. This is a constraint among attributes of a relation, not among tables or rows as entities.

Step-by-Step Solution:

Verification / Alternative check:
Armstrong’s axioms and normalization proofs always reason over attribute sets.

Why Other Options Are Wrong:
Tables / relations / rows: While FDs apply to a relation schema, the relationship itself is among attributes inside that schema.
Indexes: Physical structures; unrelated to the logical constraint definition.

Common Pitfalls:
Thinking FDs are about table-to-table relationships; that is the role of referential integrity via foreign keys.

Final Answer:
attributes.