[erlang-questions] Best practices in gen_fsm usage

[Ulf Wiger]

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

BR,
Ulf W
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