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Reading a Sequence Diagram
publish date: 2026/06/12 07:12:26.060753 UTC
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In the sequence diagram below showing the 'Report weather' interaction for the weather station, what does a stick arrowhead (as opposed to a squared-off arrowhead) on a sent message indicate?
Correct Answer
The sending object does not wait for a reply and can carry on with other processing (asynchronous message)
Explanation
In UML sequence diagrams, a stick arrowhead indicates that the sending object does not suspend itself waiting for a reply - it can carry on with other processing (asynchronous message). A squared-off (filled) arrowhead indicates that the sending object instance waits for a reply (synchronous/blocking call). In the weather station sequence, SatComms uses stick arrows when sending reportWeather() because it does not suspend itself waiting.
Reference
Software Engineering, Ian Sommerville, 10th edition