Re: [SCXML] Querying if an event would cause a transition
On 7/24/07, Christopher Giblin <[EMAIL PROTECTED]> wrote:
Hi,
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:
transitionDetector.reset();
fsmExecutor.triggerEvent(ev);
System.out.println("Transition : " + transitionDetector
.isTransitionOccurred());
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
back.
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].
-Rahul
[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
transition,
> >> without that transition occuring? Including evaluation of transition
> >> conditions?
> >
> >
> > While the idea is interesting, we do not have such an "introspection
mode".
> >
> > 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
release.
>
> > 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
>
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
Re: [SCXML] Querying if an event would cause a transition
Hi,
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:
transitionDetector.reset();
fsmExecutor.triggerEvent(ev);
System.out.println("Transition : " + transitionDetector
.isTransitionOccurred());
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
back.
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
transition,
> >> without that transition occuring? Including evaluation of transition
> >> conditions?
> >
> >
> > While the idea is interesting, we do not have such an "introspection
mode".
> >
> > 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
release.
>
> > 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
>
Re: [SCXML] Querying if an event would cause a transition
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 transition, >> without that transition occuring? Including evaluation of transition >> conditions? > > > While the idea is interesting, we do not have such an "introspection mode". > > 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 release. > 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
Re: [SCXML] Querying if an event would cause a transition
Thanks for the clarification! I digressed when I thought about transitions in action states and I see the discussion was about transitions in stable states. -Nestor - Original Message From: Rahul Akolkar <[EMAIL PROTECTED]> To: Jakarta Commons Users List Sent: Monday, July 2, 2007 12:58:15 PM Subject: Re: [SCXML] Querying if an event would cause a transition On 7/2/07, Nestor Urquiza <[EMAIL PROTECTED]> wrote: > Hi Rahul, > > In "Action States" you do have custom actions with side effects and they > result in variables part of guard transitions that will decide the final > stable state. I am talking about SCXML used as WEB Controller of course, in > other domains it could be like you just said but not in WEB where being used > as Controller, "actions" are needed and they of course are not side effect > free. > > Do you agree? > Sure. But we're digressing, we were talking about the act of figuring out which transitions would be followed, not actually following any transition (or executing any custom action) at all. We were only discussing the act of determining the first transition(s) to be followed (the cascading effect of that transition leading to an action state and further transitions out of that action state is out of scope). -Rahul > If not, could you please provide a "side effect free" implementation of the > following use case? > > 1. User is subscribing to a service using a WEB application. It is mandatory > to send a password to his cellphone to verify the user is who he says. > 2. If the password is succesfully sent, the final state will be PIN_SENT. > 3. If for the contrary the password cannot be sent the FSM will stay in the > current state USER_PROFILED. > > We talked before about action states to solve postconditions. The > introspection mechanism would work simply fine for preconditions but not for > postconditions IMHO. > > Thanks, > > -Nestor > > - Original Message ---- > From: Rahul Akolkar <[EMAIL PROTECTED]> > To: Jakarta Commons Users List > Sent: Thursday, June 28, 2007 12:54:48 PM > Subject: Re: [SCXML] Querying if an event would cause a transition > > On 6/28/07, Nestor Urquiza <[EMAIL PROTECTED]> wrote: > > Hi, > > > > Not to mention that some custom actions could have to be evaluated before > > knowing which transition will apply. > > > > It might mean that some side effects could come into scene, and if they do > > the "introspection mode" cannot be used. > > > > > Actions aren't executed unless a transition is actually followed, so > we should be OK there. However, the guard conditions on candidate > transitions would need to be evaluated, and they would need to be > side-effect free (as they should be). > > In other words, the act of identifying which transition(s) should be > followed is idempotent. > > -Rahul > > > > Thanks, > > > > -Nestor > > > > - Original Message > > From: Rahul Akolkar <[EMAIL PROTECTED]> > > To: Jakarta Commons Users List > > Sent: Wednesday, June 27, 2007 11:05:54 AM > > Subject: Re: [SCXML] Querying if an event would cause a transition > > > > Please prefix the email subject with [SCXML], since this mailing list > > is shared across all Commons components. I've added the prefix here. > > > > 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 transition, > > > without that transition occuring? Including evaluation of transition > > > conditions? > > > > > > While the idea is interesting, we do not have such an "introspection mode". > > > > 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 release. > > > > 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 :-) > > > > -Rahul > > > > > > > Thanks, > > > chris > > > > > > - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Sucker-punch spam with award-winning protection. Try the free Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/features_spam.html - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [SCXML] Querying if an event would cause a transition
On 7/2/07, Nestor Urquiza <[EMAIL PROTECTED]> wrote: Hi Rahul, In "Action States" you do have custom actions with side effects and they result in variables part of guard transitions that will decide the final stable state. I am talking about SCXML used as WEB Controller of course, in other domains it could be like you just said but not in WEB where being used as Controller, "actions" are needed and they of course are not side effect free. Do you agree? Sure. But we're digressing, we were talking about the act of figuring out which transitions would be followed, not actually following any transition (or executing any custom action) at all. We were only discussing the act of determining the first transition(s) to be followed (the cascading effect of that transition leading to an action state and further transitions out of that action state is out of scope). -Rahul If not, could you please provide a "side effect free" implementation of the following use case? 1. User is subscribing to a service using a WEB application. It is mandatory to send a password to his cellphone to verify the user is who he says. 2. If the password is succesfully sent, the final state will be PIN_SENT. 3. If for the contrary the password cannot be sent the FSM will stay in the current state USER_PROFILED. We talked before about action states to solve postconditions. The introspection mechanism would work simply fine for preconditions but not for postconditions IMHO. Thanks, -Nestor - Original Message From: Rahul Akolkar <[EMAIL PROTECTED]> To: Jakarta Commons Users List Sent: Thursday, June 28, 2007 12:54:48 PM Subject: Re: [SCXML] Querying if an event would cause a transition On 6/28/07, Nestor Urquiza <[EMAIL PROTECTED]> wrote: > Hi, > > Not to mention that some custom actions could have to be evaluated before knowing which transition will apply. > > It might mean that some side effects could come into scene, and if they do the "introspection mode" cannot be used. > Actions aren't executed unless a transition is actually followed, so we should be OK there. However, the guard conditions on candidate transitions would need to be evaluated, and they would need to be side-effect free (as they should be). In other words, the act of identifying which transition(s) should be followed is idempotent. -Rahul > Thanks, > > -Nestor > > - Original Message > From: Rahul Akolkar <[EMAIL PROTECTED]> > To: Jakarta Commons Users List > Sent: Wednesday, June 27, 2007 11:05:54 AM > Subject: Re: [SCXML] Querying if an event would cause a transition > > Please prefix the email subject with [SCXML], since this mailing list > is shared across all Commons components. I've added the prefix here. > > 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 transition, > > without that transition occuring? Including evaluation of transition > > conditions? > > > While the idea is interesting, we do not have such an "introspection mode". > > 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 release. > > 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 :-) > > -Rahul > > > > Thanks, > > chris > > > > - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [SCXML] Querying if an event would cause a transition
Hi Rahul, In "Action States" you do have custom actions with side effects and they result in variables part of guard transitions that will decide the final stable state. I am talking about SCXML used as WEB Controller of course, in other domains it could be like you just said but not in WEB where being used as Controller, "actions" are needed and they of course are not side effect free. Do you agree? If not, could you please provide a "side effect free" implementation of the following use case? 1. User is subscribing to a service using a WEB application. It is mandatory to send a password to his cellphone to verify the user is who he says. 2. If the password is succesfully sent, the final state will be PIN_SENT. 3. If for the contrary the password cannot be sent the FSM will stay in the current state USER_PROFILED. We talked before about action states to solve postconditions. The introspection mechanism would work simply fine for preconditions but not for postconditions IMHO. Thanks, -Nestor - Original Message From: Rahul Akolkar <[EMAIL PROTECTED]> To: Jakarta Commons Users List Sent: Thursday, June 28, 2007 12:54:48 PM Subject: Re: [SCXML] Querying if an event would cause a transition On 6/28/07, Nestor Urquiza <[EMAIL PROTECTED]> wrote: > Hi, > > Not to mention that some custom actions could have to be evaluated before > knowing which transition will apply. > > It might mean that some side effects could come into scene, and if they do > the "introspection mode" cannot be used. > Actions aren't executed unless a transition is actually followed, so we should be OK there. However, the guard conditions on candidate transitions would need to be evaluated, and they would need to be side-effect free (as they should be). In other words, the act of identifying which transition(s) should be followed is idempotent. -Rahul > Thanks, > > -Nestor > > - Original Message > From: Rahul Akolkar <[EMAIL PROTECTED]> > To: Jakarta Commons Users List > Sent: Wednesday, June 27, 2007 11:05:54 AM > Subject: Re: [SCXML] Querying if an event would cause a transition > > Please prefix the email subject with [SCXML], since this mailing list > is shared across all Commons components. I've added the prefix here. > > 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 transition, > > without that transition occuring? Including evaluation of transition > > conditions? > > > While the idea is interesting, we do not have such an "introspection mode". > > 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 release. > > 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 :-) > > -Rahul > > > > Thanks, > > chris > > > > - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Take the Internet to Go: Yahoo!Go puts the Internet in your pocket: mail, news, photos & more. http://mobile.yahoo.com/go?refer=1GNXIC - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [SCXML] Querying if an event would cause a transition
On 6/28/07, Nestor Urquiza <[EMAIL PROTECTED]> wrote: Hi, Not to mention that some custom actions could have to be evaluated before knowing which transition will apply. It might mean that some side effects could come into scene, and if they do the "introspection mode" cannot be used. Actions aren't executed unless a transition is actually followed, so we should be OK there. However, the guard conditions on candidate transitions would need to be evaluated, and they would need to be side-effect free (as they should be). In other words, the act of identifying which transition(s) should be followed is idempotent. -Rahul Thanks, -Nestor - Original Message From: Rahul Akolkar <[EMAIL PROTECTED]> To: Jakarta Commons Users List Sent: Wednesday, June 27, 2007 11:05:54 AM Subject: Re: [SCXML] Querying if an event would cause a transition Please prefix the email subject with [SCXML], since this mailing list is shared across all Commons components. I've added the prefix here. 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 transition, > without that transition occuring? Including evaluation of transition > conditions? While the idea is interesting, we do not have such an "introspection mode". 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 release. 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 :-) -Rahul > Thanks, > chris > > - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [SCXML] Querying if an event would cause a transition
Hi, Not to mention that some custom actions could have to be evaluated before knowing which transition will apply. It might mean that some side effects could come into scene, and if they do the "introspection mode" cannot be used. Thanks, -Nestor - Original Message From: Rahul Akolkar <[EMAIL PROTECTED]> To: Jakarta Commons Users List Sent: Wednesday, June 27, 2007 11:05:54 AM Subject: Re: [SCXML] Querying if an event would cause a transition Please prefix the email subject with [SCXML], since this mailing list is shared across all Commons components. I've added the prefix here. 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 transition, > without that transition occuring? Including evaluation of transition > conditions? While the idea is interesting, we do not have such an "introspection mode". 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 release. 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 :-) -Rahul > Thanks, > chris > > - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Got a little couch potato? Check out fun summer activities for kids. http://search.yahoo.com/search?fr=oni_on_mail&p=summer+activities+for+kids&cs=bz - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: [SCXML] Querying if an event would cause a transition
Please prefix the email subject with [SCXML], since this mailing list is shared across all Commons components. I've added the prefix here. 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 transition, without that transition occuring? Including evaluation of transition conditions? While the idea is interesting, we do not have such an "introspection mode". 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 release. 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 :-) -Rahul Thanks, chris - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
