Study Cards on starts, wait, time

UML supports the ability to set .... To cause behaviors to kick off when the correct time arrives
UML supports the ability to set  Timers/Alarms To cause behaviors to kick off when the correct time arrives
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The Wait for Time Event looks like ....?
a pair of triangles in the shape of an old-fashioned hourglass

Underneath the node is an indication when the timer should expire.
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When is the Wait for Time triggered?
It is triggered when an edge and its token arrive at the node (usually from the left).

Underneath the node is an indication when the timer should expire.

It could be a specific time, though usually it is a time relative to the cycle of the ongoing activity. It could also be a repeating time, e.g., every 2 minutes
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What is an Send Message?
  • It is an Executable Node

  • Send Event: This action starts when all its input edges are populated. If there are no input edges, it starts when the enclosing region is entered


  • Send Message: When the action starts, it emits a signal by the specified name that may be accepted by a similarly named reception elsewhere (See row 3 of this table). Usually used for cross-task communication

  • If there is an output edge, a control token is output so that it can be considered finished
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What is an Wait for Message?
  • It is an Executable Node



  • Wait for Event:  This wait action starts when all its input edges are populated, or if there are no input edges, it starts when the enclosing region is entered


  • Wait for Message:  When the action starts, it waits for a signal (message) by the specified name.

  • Receive Event:  The entity holding this node must be an active classifier with the signal listed in its reception compartment


  • Receive Message: When the proper signal arrives, the contents of the signal (if any) are emitted along with a token on the output edge
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What is this pair of rectangle -hour glass symbol?
An Wait for Time symbol
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When does this Wait for Event start?
Another way of starting a Wait for Time Event is not to have any explicit starting edge.

In such cases, as soon as the containing region is entered, the wait starts executing.

As long as the region is active, the Wait for Time Event will restart.

This produces a timing pattern with a constant time between successive starts of ReadSensor as shown in the bottom part of Fig. 16.22
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