UML 2.0 in a Nutshell

Sequence Timing

UML provides a notation to capture a specific time associated with an event occurrence. You simply place a small horizontal line next to an event occurrence to capture the time of the occurrence, or place a timing constraint on it. Typically, you use a variable to capture a specific instance in time and then represent constraints as offsets from that time. Constraints are expressed like state invariants and placed next to the event occurrence.

For example, if you want to express that a credit card authorization system must return approval or denial within three seconds of placing the request, you can place time constraints on the event occurrence, as shown in Figure 10-37.