Re: [boost] Re: Re: Some questions on the FSM submission

From: Scott Woods (scottw_at_[hidden])
Date: 2003-06-05 17:46:32

> ---------------------------
> event <-> signal
> reaction <-> input
> guard(ed reaction) <-> constrained input
> junction point/choice point <-> decision
> entry action <-> initialisation
> exit action <-> finalisation
> state with two or more orthogonal regions <-> state aggregation
> inner state <-> composite state
> terminator <-> stop state

awesome.

>
> The remaining concepts (transition, deferral) have the same names in both
> languages.
> Interestingly, SDL also defines exception handlers (supported by
> boost::fsm), which UML lacks completely.

yes. not sure whether thats a plus for SDL or UML ;-)

>
> Moreover, SDL specifies block and process agents, which are not supported
by
> UML and my library but could be implemented on top of it.
>
> I therefore think that boost::fsm could be useful for domains where
behavior
> is specified with SDL.

absolutely!

reading your summary (of UML/SDL comparison) has been
interesting. for me it has exposed the fact that some concepts are
"missing" from both UML and SDL (hope those folks aren't listening
to this ;-). to some extent i have fooled myself that SDL is "better
directed" at specification of communities of FSMs. at a language
level you have shown that they are in fact very similar (not totally). to
some
degree its probably historical that SDL has been adopted by telecoms (large
distributed communities of FSMs) and UML has been adopted by
the "desktop-software" community (i use an extreme term to make
a point only). so maybe my misconception is related to the typical
application of SDL and the tools that have been developed around
the standard. check out;

http://www.telelogic.com/products/additional/objectgeode/index.cfm

this is a product i used a few years ago. its a pretty complete
"implementation"
of SDL - you draw SDL, push a button and it generates the target system
in C (that's what the brochures say ;-). it is very much targeted at large
communities of FSMs.

the sort of thing that i queried a while ago (and i think related to what
chris was
asking) was; "where is the [separate] definition of the protocols"? right or
wrong
i believe that FSMs interact through sending of signals (presentation of
events?).
this interaction is a protocol and a protocol has its own "existence" - it
is not
owned by the FSMs. neither UML or SDL highlights this. using SDL i was
certainly able to implement protocols but it would have been a royal pain to
uplift that "protocol" and reuse it in another project.

understand your current targets and look forward to review (and acceptance
;-).
if you still have some energy left over after all of that, i might mention
the protocol
thing again. but only if your begging for more punishment.

> How is that code usually implemented? Are there SDL code generators and/or
> widely used libraries or do people normally handcraft such systems?

usually? i would say using "handcrafted" state-machine code. there are a
bunch of SDL tools but only a few generators and none of these were cheap
(think 10s of thousands) around the time i knew about such things. telcos
have
large budgets for implementation of signaling systems and the vendors price
accordingly ;-)

hope that was lucid and thanks,
scott