Section 9.6. A Participant s State-Line

9.6. A Participant's State-Line

Now that you have added time to the timing diagram (fancy that!), you can show what state a participant is in at any given time. If you take a look back at Figure 9-6 and Figure 9-7, you can already see how participant's current state is indicated: with a horizontal line that is called the state-line.

At any given time in the interaction, a participant's state-line is aligned with one of the participant's states (see Figure 9-9).

Figure 9-9. In this example, p1:Participant's state-line indicates that it is in State1 for 1 unit of time, State2 for three units of time, and State3 for roughly five units of time (before returning to State1 at the end of the interaction)

Figure 9-10 shows how the Create a new Regular Blog Account timing diagram is updated to show the state of each participant at a given time during the interaction.

In practice, you would probably add both events and states to a timing diagram at the same time. We've split the two activities here simply because it makes it easier for you to see how the two pieces of notation are applied (without confusing one with the other).

That's all there is to showing that a participant is in a specific state at a given time. Now it's time to look at why a participant changes states in the first place, which leads us neatly to events and messages.

Figure 9-10. Each of the participants needs to have a corresponding state-line to indicate their state at any given point in time