A specialization constraint states that an entity instance must belong to only one subtype and must belong to some subtype. Which classification is this?

Introduction / Context:
Specialization constraints define how instances of a supertype are allocated among subtypes. There are two axes: disjoint versus overlap, and total versus partial. This question combines both to describe a common rule set.

Given Data / Assumptions:

• Only one subtype membership is allowed for any instance.
• Membership in at least one subtype is required.
• We must map these conditions to the standard constraint names.

Concept / Approach:
Disjoint means an instance can be in only one subtype. Overlap would allow simultaneous membership in multiple subtypes. Total specialization means each supertype instance must be in at least one subtype. Partial specialization means some supertype instances may be in no subtype.

Step-by-Step Solution:

Verification / Alternative check:
Diagramming tools often display this combination with a disjoint marker (often a letter d) and a total double line constraint from supertype to subtypes.

Why Other Options Are Wrong:

• Disjoint with partial: allows only one subtype but does not require belonging to any subtype.
• Overlap variants: contradict the “only one subtype” rule because they allow multiple memberships.

Common Pitfalls:
Confusing total with disjoint. Disjoint concerns exclusivity across subtypes; total concerns coverage of the supertype population.

Final Answer:
Disjoint with total specialization