Does cardinality in ER modeling specify how many instances of one entity can (or must) be associated with each instance of another entity (for example, 1:1, 1:N, or M:N)?

Introduction / Context:
Cardinality is a foundational ER concept that communicates the numeric mapping between entity instances: one-to-one, one-to-many, or many-to-many. It is essential for correct logical design and physical implementation (keys and foreign keys).

Given Data / Assumptions:

• We are considering standard ER notation with cardinality and optionality.
• Examples: each Order is placed by exactly one Customer (N:1), each Course can have many Students (1:N), and each Student can enroll in many Courses (M:N).
• Optionality (mandatory vs. optional participation) is related but distinct from cardinality.

Concept / Approach:
Cardinality answers “how many” instances on one side can or must relate to one instance on the other. Optionality answers “must there be at least one?” Both are captured in good modeling notations. The definition in the prompt matches the accepted meaning of cardinality.

Step-by-Step Solution:

Verification / Alternative check:
Compare with any ERD legend: the definitions of 1:1, 1:N, and M:N explicitly reference counts per instance.

Why Other Options Are Wrong:

• Incorrect: denies the standard definition.
• “Only optionality” is wrong; optionality is separate from counts.
• Binary-only: while commonly applied to binaries, the idea of participation counts generalizes with care to n-ary relationships.

Common Pitfalls:
Confusing optionality with cardinality; overlooking that cardinality drives key placement and normalization.

Final Answer:
Correct