Properties of a well-formed relation (table) in the relational model: Which statement is true for every relation?

Introduction / Context:
Relational tables obey certain structural properties that simplify querying and ensure clarity. Recognizing these properties helps avoid design mistakes and ambiguous schemas.

Given Data / Assumptions:

• Relations are named structures consisting of attributes (columns) and tuples (rows).
• Schema-level naming and constraints matter for correctness and usability.
• Set semantics reduce reliance on ordering.

Concept / Approach:

Every relation must have a unique name within its schema/database catalog to avoid ambiguity. Rows should be unique (enforced logically by keys), and column names must be unique within a table to reference them unambiguously. Row and column order is not semantically significant in relational theory (SQL implementations may display a default order, but semantics do not depend on it).

Step-by-Step Solution:

Verification / Alternative check:

Attempt to create two tables with the same name; the DBMS rejects duplicates. Attempt to reference ambiguous column names; SQL requires disambiguation or prohibits duplicates in the same table.

Why Other Options Are Wrong:

Rows “not unique”: incorrect—keys enforce uniqueness.

Duplicate attribute names: invalid; leads to ambiguity.

Column order significant: relational semantics do not depend on order.

Common Pitfalls:

Relying on implicit row order in queries; always use ORDER BY to define output order.

Final Answer:

Each relation has a unique name.