Arity of relationships In data modeling, a binary relationship refers to:

Introduction / Context:
Relationships in ER modeling are categorized by arity: unary (recursive), binary, and ternary (or n-ary). Understanding the arity helps you decide how to implement the association in a relational schema, especially when moving from conceptual to logical and physical designs.

Given Data / Assumptions:

• We distinguish relationships (between entities) from attributes (properties of entities).
• Binary means two participants; unary means one (self-relationship); ternary means three.
• Cardinality (1 or many) is separate from arity.

Concept / Approach:

A binary relationship involves exactly two entity types. Examples include Customer–Order, Student–Course, and Employee–Department. Cardinalities such as 1:1, 1:N, or M:N specify how many instances on each side may or must participate, but they do not change the fact that there are two participating entity types.

Step-by-Step Solution:

Verification / Alternative check:

Most modeling guides define arity precisely; binary is by far the most common and is often implemented with foreign keys (1:1 or 1:N) or associative tables (M:N).

Why Other Options Are Wrong:

• Option A conflates attribute relationships with entity associations.
• Options C and D refer to participation counts but not to arity.
• Option E specifies a particular cardinality, not the arity.

Common Pitfalls:

• Mislabeling recursive relationships (unary) as binary because two rows are involved.
• Assuming M:N means ternary; it is still binary if only two entity types are involved.

Final Answer:

An association between exactly two entities