The sequence diagram given in Figure 1 for the Weather Information System takes place when an external system requests the summarized data from the weather station. The increasing order of lifeline for the objects in the system are:
1
Sat comms → Weather station -→ Commslink → Weather data
2
Sat comms → Comas link → Weather station → Weather data
3
Weather data → Comms link → Weather station → Sat Comms
4
Weather data → Weather station → Comma link —> Sat Comma