An AcceptEventAction with the Trigger::port set to be iKeypad:I_Keypad unmarshalls a S_Digit signal to extract the digit:Integer. It then sends this to the append operation of its number:Number.

The number:Number also provides the accumulated digits so far as a String. This String is printed prefixed with the id of the receiver (so we can see which one was connected). And the String is then sent out via the oDisplay:~I_Display Port.

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The Append activity within Number

Notes

[COMPLICATION]{INFORMATIVE} UML/SysML: When sending a Signal (message) via a Port the 'target' is the owner of the Port through which the message will be sent, it is NOT the final recipient! So the 'target' is essentially the "sender"!

Snippets (quotes/extracts)

[UML-2.5.1] InvocationAction::onPort : Port [0..1] For CallOperationActions, SendSignalActions, and SendObjectActions, an optional Port of the target object through which the invocation request is sent.

[UML-2.5.1] SendSignalAction::target: The InputPin that provides the target object to which the Signal instance is sent