Clarify the definition of a ternary relationship in ER modeling: does “ternary” mean two entities plus one association, or something else?

Introduction / Context:
Relationship degree is a precise term in ER modeling. Unary (degree 1) involves one entity type (recursive relationship), binary (degree 2) involves two, and ternary (degree 3) involves three. The question challenges a common misunderstanding of “ternary.”

Given Data / Assumptions:

• We are modeling at the conceptual level with standard ER notation.
• “Association” refers to the relationship itself connecting entities.

Concept / Approach:
A ternary relationship connects three entity types simultaneously in a single relationship instance. Its semantics cannot generally be decomposed into independent binary relationships without potentially losing constraints. For example, Supplier–Part–Project as a ternary “supplies” relationship captures which supplier supplies which part to which project at once.

Step-by-Step Solution:
Define relationship degree: number of entity types participating.Map “ternary” to degree 3 → requires three entity types.Evaluate the statement claiming “two entities and one association.”Conclude it is incorrect; two entities form a binary relationship, not a ternary one.

Verification / Alternative check:
Attempt to model supplier–part–project as three binaries; you will not enforce that the same supplier–part pair applies to a specific project without additional constraints, hence the need for a ternary relationship.

Why Other Options Are Wrong:
“Valid” is false; “recursive” does not change the degree count; “physical design” is unrelated; “ambiguous” is unnecessary—degree has a clear definition.

Common Pitfalls:
Assuming any relationship can be decomposed into binaries without loss; miscounting degree when one entity appears twice (that is still unary or binary depending on context).

Final Answer:
Invalid statement — a ternary relationship involves three entity types in one relationship