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From Rahul Akolkar <>
Subject Re: [scxml] update datamodel from java
Date Sat, 04 Sep 2010 17:44:16 GMT
On Sat, Sep 4, 2010 at 1:19 PM, Azraiyl <> wrote:
> Thanks for your response. Just out of curiousity: Is this the intended
> behaviour of SCXML?
> Chapter 3.3.3: If the "event" clause is missing, the transition is
> taken whenever the "cond" evaluates to true.

At a high level, the only way for the environment to communicate with
a state machine is through events. Data model changes are best made
via native mechanisms described in state machine theory (such as event
payloads). Doing so will cause the "cond" to be evaluated in the
process and has the additional benefit of being more declarative (i.e.
it will be modeled with the rest of the state machine, rather than
behavior that can't be noticed just by reading the SCXML document).

Programmatic access to the data model (only root context is
accessible) is provided as this is often convenient in certain
environments. However, such access clearly isn't portable across
implementations and has the downsides of not being tied into the event
processing loop. If such a choice is made by the developer, there is
an additional onus on the developer -- this includes, firing an event
if need be and synchronizing access if needed etc.

IMO, the section 3.3.3 quote probably needs some sort of disclaimer
for programmatic access. There are cases where the application may
deem it unnecessary for every programmatic update to the root context
to result in evaluating all conds. Commons SCXML provides the
developer that level of control.


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