Where are interaction use messages expected to enter or leave?

Interaction use messages are expected to enter or leave through gates on the model boundary because these gates represent the points of interaction between a system and its environment or between different parts of a system. Gates serve as the interface for exchanging messages, enabling communication between different components, interactions, or systems.

In modeling, representing gates clearly indicates where messages can be sent or received, allowing modelers to visualize the flow of information and the interactions that occur. This is crucial for defining the behavior of interacting elements within a system, as it establishes the boundaries of where messages can enter or exit, ensuring that interactions are well-structured and manageable.

Model boundary gates reinforce the concept of encapsulation, aiding in the understanding of how different parts of a model interface with each other while maintaining clarity on where interactions begin and end. This is vital for accurate representations of systems and for ensuring that the model is both understandable and functional.