In entity–relationship modeling, for any given relationship between two entities, how many possible sets of minimum cardinalities exist across the pair?

Introduction / Context:
Cardinality in ER modeling expresses how many instances of one entity can or must relate to instances of another entity. Minimum cardinality captures the “optionality” requirement—whether participation is required (1) or optional (0).

Given Data / Assumptions:

• Two entities participate in a relationship.
• Each side's minimum cardinality can be 0 (optional) or 1 (mandatory).

Concept / Approach:
For two entities A and B, each side has two possibilities for minimum cardinality: 0 or 1. The combination count equals the product of possibilities: 2 * 2 = 4. The four specific sets are (0,0), (0,1), (1,0), and (1,1).

Step-by-Step Solution:

Verification / Alternative check:
Any ER diagramming method that uses mandatory/optional marks per side implicitly supports these four cases.

Why Other Options Are Wrong:
Two/Three/Six: Do not cover all paired combinations of two binary choices.

Common Pitfalls:
Confusing minimum cardinality with maximum cardinality (1 or many). Minimum cardinality is about required participation, not quantity caps.

Final Answer:
Four