In relational database design, what do we call a group of one or more attributes (columns) that uniquely identifies a single row (tuple) in a table?

Introduction / Context:
Relational databases rely on identifiers to distinguish one row from another. The concept that captures this ability to uniquely pinpoint a row is fundamental to normalization, integrity constraints, and query optimization.

Given Data / Assumptions:

• A “row” is also called a tuple.
• An “attribute” is a column in a relation (table).
• One or more attributes may be needed to uniquely identify a row.
• We are working within standard relational theory terminology.

Concept / Approach:
A set of attributes that uniquely identifies tuples is called a key. If the key is minimal (no proper subset is a key) it is a candidate key; once chosen for identification, it becomes the primary key. A set that is not minimal but still uniquely identifies rows is a superkey.

Step-by-Step Solution:

Verification / Alternative check:
Texts on relational theory define key/superkey/candidate key precisely as uniqueness constraints over attributes; this aligns with the prompt.

Why Other Options Are Wrong:
Determinant: Any attribute set on the left side of a functional dependency; not necessarily unique for all rows.
Tuple: A row, not the identifier of a row.
Relation: A table, not its identifier.
Composite attribute: An attribute made of components; unrelated to uniqueness by itself.

Common Pitfalls:
Confusing “determinant” with “key”; determinants may not be minimal or unique across the entire relation.

Final Answer:
Key