On 03/12/2012 16:02, Jacob Beard wrote:
Hi Francesco,
Hi Jacob,
thanks for your solution that I've read with interest. First of all,
your solution has a minor issue I'm concerned about:
- in Statecharts, AFAIK, the notion of timeout implies that something
must be executed after a known amount of time; in the semantics I've in
mind, borrowed from Timed Automata, a transition is enabled/disabled in
certain time-windows. This means that nothing *happens* but something
*can happen* (non deterministically) when the condition is true ... but
this may be a minor issue, because it happened that our work stemmed
from Timed Automata
A major concern we have is that right now we have in mind more complex
expressions. For instance, at the moment we consider two kinds of
conditions on transitions:
- time conditions that enable/disable a transition;
- a conjunctive boolean formula, that refers to a finite set of
propositions in description logic;
- a combination of the above two.
This apparently heterogeneous language is aimed at describing
parametrized FSMs (i.e. FSM with an undefined number of running
"instances") to reason on timed and RESTful services. Due to the fact
that the research project is a work-in-progress, the "shape" of those
expressions are not yet definitive and may change, so we'd figure
leveraging the flexibility of SCXML (in particular its datamodel) would
give us a more "stable" ground to work on, possibly re-using the base
Apache Commons libraries and Eclipse editor, and maybe extend it.
-FS
The example you describe looks like the special "timeout" event described
by Harel in his original papers on Statechart semantics:
http://research.microsoft.com/apps/pubs/default.aspx?id=148785
http://dl.acm.org/citation.cfm?id=235322
If so, this event can be implemented in SCXML as a transformation, as in
the following example: https://gist.github.com/4195449
In this example, on entering state "a", the event "$timeout_1" is scheduled
to be sent after 1 second. If the state is exited before that time, the
scheduled event will be cancelled via the <cancel> action. If the machine
stays in state "a", and after 1 second the event is sent, then the
transition in state "a" with event "$transition_1" will be selected, and
the machine will leave state "a" and enter state "b".
This transformation can be implemented easily in a language like XSLT.
Therefore, SCXML should be able to handle your example out of the box. Does
your application have other, more complex requirements for transition
conditions?
Jake
On Mon, Dec 3, 2012 at 9:30 AM, Francesco Spegni <francesco.spe...@gmail.com
wrote:
The first problem we are trying to solve is: how to extend the definition
of Transition to accept custom XML nodes to be interpreted as complex
conditions? E.g. we would like to express something as:
<scxml xmlns="http://www.w3.org/2005/**07/scxml<http://www.w3.org/2005/07/scxml>
"
version="1.0"
initialstate="a"
datamodel="xmlns:cc="someurl" >
<state id="a">
<transition target="b" cond="cc:eval(//condition)" >
<cc:condition>
<time exp="clock > 1 sec" />
</cc:condition>
</transition>
</state>
<state id="b" final="true">
</state>
</scxml>
--
Francesco Spegni
"Ama le nuvole, le macchine, i libri, ma prima di tutto ama l'uomo" -
Nazim Hikmet
http://www.manuefra.eu
skype: francesco.spegni
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