[boost] [msm] history pseudo states

Subject: [boost] [msm] history pseudo states
From: Michael Caisse (boost_at_[hidden])
Date: 2009-12-06 21:21:31

Hello Christophe -

I am trying to understand your implementation of history. In the
MSM documentation it states:

"As explained in the BoostCon09 paper <cid:part1.00040908.05020506_at_[hidden]>, Histories are weird. First,
there can be just one."

In the boostcon09 paper it also states [page 5]:

"To be frank, History is not a completely satisfying concept. First
of all, there can be just one history pseudostate and only one 
transition may originate from it."

I'll not contend with the views of history yet. They can be a very
powerful concept. What I'm unclear about is the statement that
there can be just one. According to the UML specification there
can be just one per composite state. That of course makes perfect
sense. MSM has SubmachineStates instead of composite states; however,
the same "rule" applies to both.

Does MSM obey this definition or is there a further constraint?
My confusion might be partially attributed to not having finished
reading all of the docs.

Thanks -
michael

-- 
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Michael Caisse
Object Modeling Designs
www.objectmodelingdesigns.com