Which of the following is not an aspect of a Use Case Diagram?

A Use Case Diagram is a visual representation that depicts the interactions between users (actors) and the system's functions within defined boundaries. The purpose of this diagram is to illustrate how users interact with the system to achieve specific goals or outcomes.

The concept of a system boundary is crucial in diagramming as it defines the scope of the system, clarifying what is included in the system and what is outside of it. Functions, or use cases, represent the various operations or services the system offers to its actors, signifying the tasks being performed. Actors are the users or external systems that interact with the system, highlighting who is involved in the use cases.

Interactions, however, are not a specified element of a Use Case Diagram in the same way. While the diagram does show relationships between actors and use cases, the term "interactions" may imply a deeper level of detail about the nature of these relationships, which goes beyond the simple representation of roles and functions. Thus, while interactions are certainly a part of the broader analysis that may involve use case scenarios and system behavior, they are not distinctly represented as a component within a Use Case Diagram itself.