[erlang-questions] Best practices in gen_fsm usage

Torben Hoffmann <>
Wed Dec 7 23:26:26 CET 2011


Adding to the SDL wagon: I have had to implement the Q.SIG standard and 
with a little thought it is possible to get Erlang code that is almost 
1:1 with the SDL diagrams - there is a little example in the EUC 2010 
presentation by Raghav Karol and me where we have one function call for 
each box in the SDL diagrams. That makes it very easy to debug the code 
in the rare case that one has done something wrong ;-)

But for creation of new software where there is no SDL specification of 
the protocols there is no real benefits of creating SDL before coding. 
For that I think that Object Process Methodology (used lightly) and 
Message Sequence Charts are better ways of structuring your high level 
thoughts.

Cheers,
Torben

On 7/12/11 18:24 , Ulf Wiger wrote:
>
> On 7 Dec 2011, at 18:04, Max Lapshin wrote:
>
>> Ulf told something about SDL, but I really don't know what is SDL.
>
> SDL = Specification and Description Language, is a ITU-T standard 
> language for describing systems of communicating state machines. This 
> was used much in Telecoms, and in real-time systems design, often 
> together with Message Sequence Charts (MSC), to produce high-level 
> systems architecture diagrams.
>
> SDL also extends down into programming with SDL/PR, but we can ignore 
> that. ASN.1 - a loosely related data description layer - is however 
> still quite relevant.
>
> In the great UML:ification, SDL was absorbed into UML. Before that, it 
> became more and more object-oriented. Still, the earlier versions are 
> actually fairly decent for describing erlang-based systems. In fact, 
> it was once shown that a system described in SDL could be mapped 1:1 
> over to Erlang. This has not been done much, since it was also easy to 
> demonstrate that the same system could be more easily described in 
> Erlang in the first place (although such a description would lose many 
> of the qualities of a good system architecture description).
>
> Here is a tutorial of sdl88. The link jumps directly into something 
> that ought to look familiar:
>
> http://www.sdl-forum.org/sdl88tutorial/4.ProcessCommunication/4.1_Signal_input_queue.htm
>
> Here's another overview:
> http://www.cs.nthu.edu.tw/~tanghome/SDTDoc/introsdl.html 
> <http://www.cs.nthu.edu.tw/%7Etanghome/SDTDoc/introsdl.html>
>
> BR,
> Ulf W
>
>
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> 
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