Input event

An input event designates the consumption of a message. Normally there is a corresponding output event. The input event follows after the corresponding output event in time.

<message in area> ::= <message in symbol>

is attached to <instance axis symbol>

is attached to <message symbol>

<message in symbol> ::= <void symbol>

The <void symbol> is a geometric point without patial extension. The <message in symbol> is actually only a point which is on the instance axis. The end of the message symbol which is the arrow head is also pointing on this point on the instance axis.