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From "Rahul Akolkar" <>
Subject Re: [SCXML] Conditional transitions into a composite state
Date Sun, 17 Sep 2006 16:56:12 GMT
On 9/15/06, Jon Brule <> wrote:
> Let me try another model to see if I can better convey what I am
> trying to do. Consider the following SCXL:

Thanks for taking time to post another example, it helped me better
understand what you were after. I see you've found one solution (in
the next email on this thread).


> <scxml xmlns=""
>        version="1.0"
>        initialstate="S1">
>   <state id="S1">
>     <initial>
>       <transition target="S11"/>
>     </initial>
>     <state id="S11">
>       <transition event="E1" target="S12"/>
>     </state>
>     <state id="S12">
>       <transition event="E2" target="S13"/>
>       <transition event="*" cond="_eventdata.mode eq 'S2'" target="S2"/>
>       <transition event="*" cond="_eventdata.mode eq 'S3'" target="S3"/>
>     </state>
>     <state id="S13">
>       <transition event="E3" target="S11"/>
>     </state>
>   </state>
>   <state id="S2">
>     <initial>
>       <transition target="S2Router"/>
>     </initial>
>     <state id="S2Router">
>       <transition cond=" eq 'E_S21'" target="S21a"/>
>       <transition cond=" eq 'E_S22'" target="S22"/>
>       <transition cond=" eq 'E_S23'" target="S23"/>
>     </state>
>     <state id="S21a">
>       <transition event="event" target="S21b"/>
>     </state>
>     <state id="S21b" final="yes"/>
>     <state id="S22" final="yes"/>
>     <state id="S23a">
>       <transition event="event" target="S23b"/>
>     </state>
>     <state id="S23b">
>       <transition event="event" target="S23c"/>
>     </state>
>     <state id="S23c" final="yes"/>
>     <transition event="S2.done" target="S13"/>
>   </state>
>   <state id="S3">
>     <initial>
>       <transition target="S3Router"/>
>     </initial>
>     <state id="S3Router">
>       <transition cond=" eq 'E_S31'" target="S31"/>
>     </state>
>     <state id="S31a">
>       <transition event="event" target="S31b"/>
>     </state>
>     <state id="S31b" final="yes"/>
>     <transition event="S3.done" target="S13"/>
>   </state>
> </scxml>
> Within this XML, I have three distinct composite states. S1 represents
> a generic engine. It has three child states that execute a certain
> standard flow. While in state S12, it is possible to call out to
> either states S2 or S3 with any event providing the corresponding mode
> has been set. If the mode is set to "S2", then any event thrown will
> transition to the S2-specific machine. The same parallel goes for the
> "S3" mode.
> My intent is to place the state machines for S2 and S3 in their own
> individual files, binding them into the engine using the <state> tag's
> "src" attribute. This effectively would separate the main engine from
> the secondary, mode-specific state machines. With this in mind, I am
> not crazy about coding the events specific to the S2 and S3 state
> machines within the S1 engine, thus my use of the event="*" attribute.
> Within each mode-specific state machine, I need to route control to
> the appropriate "task". For example, if the engine's mode is set to
> "S2" and the "E_S21" event is thrown from within the engine's S12
> state, then control is transitioned to S21a; however, this is not
> determined by the configuration within the S1 engine. Instead, it is
> delegated to the S2 state machine which has an inbound event router,
> which in turn passes it to the appropriate substate.
> The sticky point for me is the "router" state within each of the
> mode-specific state machines. The S2Router needs to be able to access
> the name of the incoming event in order to properly route it to the
> appropriate task substate. Again, I do not want to code any
> event-specific information from the S2 state machine within the S1
> engine. It would be nice if I could access the current event from
> within the _eventdata collection, but it does not sound like it is
> currently in there. Is there another place from which I can obtain the
> current event? Would it be appropriate to add the current event into
> the _eventdata collection for a usage such as this?
> Finally, I would love to use final states within the mode-specific
> state machines to generically return to the engine. From S2's
> perspective, I see that I can encode final="yes" onto any substate and
> configure a transition directly within the S2 state machine to catch
> the S2.done event and pass it on appropriately. Ideally, I would not
> like to encode a specific S1 engine state within S2. Instead, I would
> love to use a history within S1 to which I could return once the
> event-specific task completes within the S2 state machine. Is this use
> of history possible?
> I hope this explanation helps to better explain what I am attempting to do.
> Assuming we can find generic binding solutions to these challenges, I
> would be happy to write this one up as a use case for the project.
> Thanks for all your help.
> Regards,
> Jon Brule

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