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Subject: Re: [boost] [MSM] Is there any interest in C++14 Boost.MSM-eUML like library which compiles up to 60x quicker whilst being a slightly faster too?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2016-02-12 13:44:32

Le 12/02/2016 12:20, Krzysztof Jusiak a écrit :
> On Thu, Feb 11, 2016 at 12:28 PM, Vicente J. Botet Escriba <
> vicente.botet_at_[hidden]> wrote:
>> It seems that we need to inspect the UML2.1 documentation to check what is
>> the specified behavior. If it is undefined, the argument in MSM would be
>> valid.
> I checked UML2.5 specification and I have found "Transition execution
> sequence" ( / page 316).
> However, there is no much info about the sequence there. It's mostly about
> that exit of the main state has to happen before entry to the target state.
> I can't find anything about when guard/action should happen in the sequence
> :/ buy it's a long document so maybe it might be found somewhere?
On page 377 I see an example where the order is clear

xS11; t1; xS1; t2; eT1; eT11; t3; eT111

Where xAAA means exit action on state AAA and eAAA entry on state AAA.
ti are actions on the segmented transitions.

Just before this example you can find

*"Transition execution sequence **
*Every Transition, except for internal and local Transitions, causes
exiting of a source State, and entering of the target State. These two
States, which may be composite, are designated as the main source and
the main target of a Transition respectively.
The main source is a direct substate of the Region that contains the
source States, and the main target is the substate of the Region that
contains the target States.
NOTE. A Transition from one Region to another in the same immediate
enclosing composite State is not allowed. Once a Transition is enabled
and is selected to fire, the following steps are carried out in order:
1. Starting with the main source State, the States that contain the main
source State are exited according to the rules of State exit (or,
composite State exit if the main source State is nested) as described
2. The series of State exits continues until the first Region that
contains, directly or indirectly, both the main source and main target
states is reached. The Region that contains both the main source and
main target states is called their least common ancestor. At that point,
the effect Behavior of the Transition that connects the
sub-configuration of source States to the sub-configuration of target
States is executed. (A “sub-configuration” here refers to that subset of
a full state configuration contained within the least common ancestor
3. The configuration of States containing the main target State is
entered, starting with the outermost State in the least common ancestor
Region that contains the main target State. The execution of Behaviors
follows the rules of State entry (or composite State entry) described
earlier. "

I believe this is clear enough.
1 exits
2 action
3 entries

>> BTW. I have a question related to local transitions. Concept seems to be
>>> nice but I don't undesrtand why exit/entry is NOT triggered only 'if the
>>> main target state is a substate of the main source'.
>>> Why this concept can't be more general? Wouldn't that be nice?
>>> s1 + e1 = s2 // exit from s1 / entry to s2
>>> s1 ^ e1 = s2 // no exit from s1 / no entry to s2
>>> A local transition will ensure that there is no exit on s1, but there
>> should be an entry in s2 if s2 is not s1.
>> You will need to have a nested examples to see the difference between an
>> external and a local transition.
> Yea, I do get it. Cheers. Do have any example when local transitions are
> useful? I see some usage for them but I struggle really to find a really
> good use case for them.
Let say that you have a state S with two sub-states S1 and S2.
While in state S, if you receive the event E1 you want to go to S1, but
don't want to execute the exit of state S. However you want to execute
the exit of S1 or S2.

S ^ E1 = S1;

Think of E1 as an event that interrupts whatever you were doing on S1 or S2.


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