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Re: SCXML : Event Generation and Dynamic Creation of Statechart

From: Gregory W. Bond <bond@research.att.com>
Date: Thu, 13 Apr 2006 10:05:41 -0400
Message-Id: <469d42e2ae900bb15a67e273ddbf5ed3@research.att.com>
Cc: "<www-voice@w3.org>" <www-voice@w3.org>, "Barnett, James" <James.Barnett@Aspect.com>
To: "<raxit@phonologies.com> <raxit@phonologies.com>" <raxit@phonologies.com>

Raxit

I agree with Jim that dynamic state creation is a bad idea. I would 
also like to clarify that ECharts does not support this concept. 
Rather, ECharts supports dynamic creation/destruction of submachine 
instances *within a state*. This approach ensures the number of states 
is fixed and therefore is amenable to analysis. This approach also has 
the advantage that the dynamic aspects of the program are part of the 
state machine and can therefore be analyzed as part of the state 
machine.

Greg

On Apr 13, 2006, at 9:57 AM, Barnett, James wrote:

> Raxit,
>   Dynamic creation of states is something that we have consciously 
> ruled
> out for SCXML.  The basic idea of state machines is that they have a
> fixed set of states. Even push-down automata, which are more powerful
> than finite state machines, have a fixed set of states, plus a dynamic
> stack.
>
> One strong advantage of having a fixed set of states is that machines
> are statically analyzable - by looking at chains of transitions, you 
> can
> determine whether there is a path from any given state to any other
> state.
>
> We therefore do not want any constructs in SCXML that involve the
> dynamic creation of states.  There is a way of handling multiple
> <invoke> at the platform layer that does not have this problem, and we
> will post a message on this topic soon.
>
> - Jim
>
>
> -----Original Message-----
> From: Sheth Raxit [mailto:raxit@phonologies.com]
> Sent: Monday, April 10, 2006 2:05 AM
> To: www-voice@w3.org; Barnett, James; bond@research.att.com;
> Alfred.S.Gilman@IEEE.org
> Subject: SCXML : Event Generation and Dynamic Creation of Statechart
>
> Respected  James,Greg,Gilman and other VBVG Members,
>
> With reference to previous posts, One of the point is to Generate Event
> and related stuff while processing <invoke>, I think that this is
> somewhat  like (or can be modeled as)  what  Greg has mentioned ( in
> this post
> http://lists.w3.org/Archives/Public/www-voice/2006JanMar/0040.html ),
> issue ,"Dynamic Creation of Statecharts".
>
> I think (but not much sure )that <invoke> can be modeled as , Dynamic
> Creation of new State (with new State-Id) and call to appropriate
> services, and as  actuall call is madeup from new state, with new
> stateid, What Gilman has suggested the concepts of Event would now 
> apply
>
> to this New-State, and this new-state now would do all the event
> handling and related stuff.
>
> when SCXML Engine hits <invoke>
> 1. Dynamically Create new state, (with unique State Id)
> 2. Make appropriate stuff to call Service,
> 3. Call the Service,
> 4. Do Event Handling for the Events arrived from services,
>
>
> Would it  be Semantically equivalent of Event-related stuff (suggested
> by Gilman),  ?
>
> Any thought on this issue ?
>
>
> Thanks,
> ---
> Raxit Sheth
>
> -- 
>
> Raxit Sheth
> Systems Software Engineer
> Raxit@Phonologies.com
>
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Received on Thursday, 13 April 2006 14:05:58 GMT

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