On 7/24/07, Christopher Giblin <[EMAIL PROTECTED]> wrote:
Update: In the  meantime, I have implemented a TransitionDetector class
which implements SCXMLListener and is registered with SCXMLExecutor.
It is only slightly odd to program:

        System.out.println("Transition : " + transitionDetector


Indeed. On the plus side, that can work off of the latest release.

That gives me a tactical solution for the time being. If I find that a
query, as suggested in my original post, really is required, I will get


I think in the longer term it will be possible to offer that feedback
via the SCXMLExecutor#triggerEvent() method(s), which currently have a
void return type (they could either return a boolean or the actual
list of transitions followed -- which could be empty).

This will require a major release (v1.0) if implemented, due to the
change in method signature. If you want to make sure this stays on the
radar, please file a ticket in JIRA [1].


[1] http://jakarta.apache.org/commons/scxml/issue-tracking.html

Thanks, chris

Christopher Giblin/Zurich/IBM wrote on 07/24/2007 12:00:36 PM:

> Hi,
> Sorry for the delayed response. My remarks below.
> > Please prefix the email subject with [SCXML], since this mailing list
> > is shared across all Commons components. I've added the prefix here.
> Thanks - I will be sure to in the future.
> > On 6/27/07, Christopher Giblin <[EMAIL PROTECTED]> wrote:
> >>
> >> Hi,
> >> I am new to Commons SCXML.
> >> Is it possible to determine whether an event would result in a
> >> without that transition occuring? Including evaluation of transition
> >> conditions?
> ><snip/>
> >
> > While the idea is interesting, we do not have such an "introspection
> >
> > It wouldn't take too much effort to implement it, but:
> > a) Would probably increase the code smell factor a tad (if in
> > introspection mode, then follow transition else just report back etc.)
> > b) Would require some API additions that might warrant a major
> > If you don't mind sharing in this public forum, why do you need such
> > introspection? The SCXML specification doesn't talk about this.
> > Understanding that interaction pattern may or may not help better
> > answer the question, we will have to see :-)
> I am using SCXML to describe allowable states for an application.
> Every event should result in a state transition. If no transition,
> then I need to raise an error. Adding error states to the state
> machine complicates it significantly. By comparison, simply
> expressing all allowable transitions is more elegant. This requires
> that the engine can be queried with  an event to determine if it
> would result in a transition. By default, SCXML ignores non-
> applicable events, remaining in the current state. Remaining in the
> same state is ok, but I need to know if an event transition occurred
> or not, as said. One approach would be to register as a listener to
> determine if a transition occurred. This results in an awkward
> programming style, however, further compounded by my app having
> perhaps hundreds of state machines. A program would be easier to
> read if one could ask the engine if the event leads to a transition.
> I also considered clone the state machine, listening and then
> triggering the event. Too much overhead, though. My code must also
> be efficient.
> Or do you see a better way of dealing with this?
> Thanks, chris
> > -Rahul

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