In UML relationships, what does aggregation represent relative to a simple association and inheritance?

Introduction / Context:
UML distinguishes several relationships: association (a generic link), aggregation (a whole–part relationship with shared lifetimes), composition (a stronger whole–part with owned lifetime), and generalization (inheritance, the is-a relationship). Understanding aggregation's meaning prevents confusing it with inheritance or composition.

Given Data / Assumptions:

• Aggregation indicates a whole–part (has-a) structure where parts can outlive the whole or be shared.
• Composition is the stronger whole–part where parts are owned and usually die with the whole.
• Inheritance (generalization) is an is-a relationship, not whole–part.

Concept / Approach:
Aggregation is a specialized association (hollow diamond) that models a part-of relationship but imposes weaker lifecycle semantics than composition. It is more specific than a plain association but “weaker” than composition. Among the provided choices, the most accurate phrasing is that aggregation expresses part-of and is a weaker form than association if we consider “strength” as lifecycle constraint beyond a simple link; in practice, many texts say “aggregation is a special (not stronger) kind of association.” The incorrect options tie aggregation to is-a (inheritance), which is wrong.

Step-by-Step Solution:

Verification / Alternative check:
Example: Team aggregates Players; players can exist without the team and can be shared across contexts historically, which fits aggregation (not composition, not inheritance).

Why Other Options Are Wrong:
Stronger form better describes composition.
Is-a is generalization, not aggregation.

Common Pitfalls:
Overusing aggregation when a plain association suffices; or using aggregation where composition is intended (ownership semantics).

Final Answer:
Expresses a part-of relationship and is a weaker form of an association relationship.