Empty Triggers

Question

I got these 3 errors when submitted the system modelling homework:

Static analysis found problems:
Forbidden element: empty triggers are not allowed (from White Initial Time)
Forbidden element: empty triggers are not allowed (from White Initial Time)
Forbidden element: empty triggers are not allowed (from White moves)

can you please explain what these mean and how can I fix them in my homework (in the attached picture)

https://1drv.ms/u/s!Ai62pjBNStKtg2IbF2Jo1pI7x3ZB?e=Vi8INV

Thank you.

Answer 1

The standard format of a label on a transition is trigger [guard] / action. From these three parts:

• The trigger is mandatory, and denotes the event upon which the transition fires. Omitting it yields the aforementioned error.
• The guard is optional, it denotes a condition, and the transition only fires if the condition evaluates to true after the trigger has fired.
• The actions are also optional, they perform some actions if the transition fires.

In your solution, you have transitions, that only have a guard, but no trigger. These transitions are nondeterministic, and can fire anytime, or none at all.