Open or closed arrowhead


The text says:

If a class instance sends a message to another class instance, draw a line with an open arrowhead …

However the diagram uses closed arrowhead everywhere. Is this a mistake, what is the rule around it?

Hi @Mustafa

This is for the asynchronous message. Asynchronous messages don’t need a reply for interaction to continue. Like synchronous messages, they are drawn with an arrow connecting two lifelines; however, the arrowhead is usually open and there’s no return message depicted.

Happy learning,