What type of constraint specifies a required time interval for a single event?

The type of constraint that specifies a required time interval for a single event is the time constraint. This is because time constraints are directly related to the timing aspects within a system and can define conditions such as deadlines, durations, and timing intervals associated with events.

Understanding time constraints is essential in systems modeling, as they allow modelers to effectively capture the temporal behavior and timing requirements of events in the system being designed. They help ensure that systems behave as expected in relation to time, which is particularly important in real-time systems or scenarios where timing affects performance or outcomes.

In contrast, the other options refer to different types of constraints: duration constraints typically relate to how long an event lasts or a process needs to take, state invariants apply to the conditions that must always be true in a given state of a model, and message constraints pertain to communication requirements between system components rather than time-based specifications. Each of these plays a unique role in systems modeling but does not specifically denote the requirement for a time interval tied to a single event like the time constraint does.