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From Thiébault Benoît <...@artenum.com>
Subject Re: [scxml] StopWatch usecase and State pattern
Date Sun, 22 Aug 2010 07:24:31 GMT
Thank you Rahul for your quick answer, I will have a look at the link you provided and at the
AbstractStateMachine class implementation.
Another question, not really related to the first one : is there a roadmap for the W3C standard
? I mean is there a planned date for the release of the final version of the specification
?
Kind regards,

Ben

Le 21 août 2010 à 19:47, Rahul Akolkar a écrit :

> 2010/8/21 Thiébault Benoît <dev@artenum.com>:
>> Hi everyone,
>> 
>> I'm starting using SCXML and there is something that I am not sure to understand
very well. In the previous applications I developed, I used an event-driven architecture :
my user interface (for instance) was triggering Events that an EventDispatcher converted into
(a) Action call(s). The mapping Event/Action(s) was declared in a separate XML file. When
I discovered SCXML I thought I could improve this architecture by declaring the Event/Action(s)
mapping in the SCXML file. There are however some points that are not very clear yet for me.
>> 
>> In the State design pattern (http://en.wikipedia.org/wiki/State_pattern), a state
is represented by a class while the actions are mapped with the methods (roughly). I though
I could thus map my events with a method of a given object.
>> 
>> But when I look at the StopWatch use case, and especially the StopWatch class (http://commons.apache.org/scxml/xref-test/org/apache/commons/scxml/env/StopWatch.html),
the whole state machine is represented by the class and each state is mapped by the methods...
In this use case, I don't see how actions are handled.
>> 
>> I mean if I have two events triggered targeting the same state, how can I handle
both events differently ? There could be two ways to go from a state A to a state B, for instance
in an application where you want to edit a text file, from the "ready" state (when the application
is ready to start) you could go to the "edit" state by opening an existing file or by creating
a new one. The targeted state is then the same, even though the way to reach it is different.
I don't know how to model this in SCXML.
>> 
>> Can someone help ?
>> 
> <snip/>
> 
> The AbstractStateMachine class is one simple pattern among many that
> may be employed to use Commons SCXML [1], and is certainly very basic.
> It does not implement the State pattern as described in the document
> you point to. The State pattern itself has limitations (requiring a
> flattened state machine), so even implementing that isn't a silver
> bullet. As someone who wants to use the State pattern, please take a
> look at the AbstractStateMachine class implementation and perform the
> changes necessary to rather implement the State pattern instead.
> 
> The higher order bit is that SCXML as a language is more powerful that
> any of these individual patterns.
> 
> -Rahul
> 
> [1] http://commons.apache.org/scxml/guide/using-commons-scxml.html
> 
> 
>> Thank you
>> Ben
>> 
>> 
> 
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