Allocations of Usage involve what kind of allocations?

The concept of "Allocations of Usage" pertains to the assignment and relationship between elements of usage within a modeling context. In this scenario, the correct choice highlights that this type of allocation involves linking one element of usage to another. This allocation allows for the understanding of how various usage elements interact or are dependent on each other, facilitating the analysis of system behavior and use-case scenarios.

When elements of usage are allocated to one another, it reflects a direct relationship that enhances the model's clarity in representing how functional requirements and user interactions are mapped to various system components. This approach is essential in systems modeling, as it ensures that all elements of usage are appropriately connected and represent realistic scenarios of how the system will operate.

The other choices do not align with the concept of "Allocations of Usage." Allocating definitions, constraints, or structural features pertains to different types of relationships within a model, focusing on definitions and characteristics rather than the specific interactions and usage dependencies that the correct choice emphasizes.