Topics

1

Uml Process / Triggering events should be avail to all children

« on: December 20, 2006, 12:09:26 am »

The exact same triggering events are repeated in the statechart diagrams in EA Model.  For example, I have a "poll" triggering event that is used heavily in my model as a triggering event for transitions in different part of the model.  My model is a complicated model with many substate machines and concurrent regions.  However, within each substate machine, this "poll" triggering event is created as its own SendSignalAction.  This is the SAME event in the system created MULTIPLE times.  These should be created ONCE in the parent hierarchy and available to all children substates because the same event is triggering transitions throughout the entire system.  The SendSignalActions should also be usable by any state transitions even if it is dragged from a child substate machine into a higher parent substate machine.

2

Uml Process / Should transition actions be able to create events

« on: December 20, 2006, 12:04:34 am »

According to Harel's original paper, the action that forms part of a transition can be a triggering event for another part of the system (pg 256 of "Statecharts: A visual formalism for complex systems").  This means that if a transition is occuring, the transition can generate triggering events to affect other parts of the system.  Extreme care must be taken so that infinite loops DO NOT occur because of this.  

An example of an infinite loop is shown below:



In this diagram, as soon as either eventA or eventB is triggered there will be an infinite loop.  This is because the triggering events generate the other triggering event as part of its transition action, which in turn affects the other concurrent region.  This very simple example is obvious to the naked eye, but cannot be detected using current automated tools.  Worst still, this may occur in more complicated projects which have many states, concurrent regions and triggering events.

EA Model only has a textual description as part of this field.  Perhaps this should be converted into a list of events so that we can accurately model this.  This is so that we can accurately tell where each triggering event is used.  Once we have this relationship then we can check for the above mentioned problem because we can then check for never ending event generation within the statechart.  This in itself is very useful because obviously an infinite loop as shown above is erronous and will cause extreme problems in an implementation.

3

Uml Process / Many Initial States in Concurrent state machine

« on: November 08, 2006, 07:43:07 pm »

When I validated a concurrent state machine I received warnings that having more than one Initial States were a statechart violation.  It accepted the first initial state but considered the rest as violations.

According to the UML standard: "A region can have at most one initial vertex." (pg 569 of ptc-06-04-02 - 2.1 Superstructure.pdf).  Since a concurrent state machine has multiple regions, we interpret this as: "A concurrent state machine has multiple regions, each having at most one initial vertex."

The book "UML 2.0 In a Nutshell" also supports this interpretation (Fig 8-8, pg 92).

Can the validation be fixed to recognise this part of the UML specification.

4

Uml Process / Trigger missing child element: Event

« on: November 08, 2006, 08:02:24 pm »

When I validate my statechart diagram, I get the following warning which I do not understand:

MVR020001 - warning (disconnected (Trigger)): disconnected is missing required child element: Event

Can anyone shed any light on what this actually means?  The transition in question just has a signal trigger called "disconnected".  If it is missing any other important specification than I'd like to know what because it seems to be a well formed UML transition.