Subject: Re: SDL-News: A question about history in SDL-2000
From: Rick Reed TSE (rickreed#tseng.co.uk)
Date: Wed Dec 19 2001 - 15:36:03 GMT
Dear Birger,
In Geneva in September you volunteered to provide an answer to the
following:
> From: Jacqueline Floch <Jacqueline.Floch#item.ntnu.no>
> Reply-To: Jacqueline Floch <Jacqueline.Floch#item.ntnu.no>
> Date: Tue, 06 Nov 2001 16:06:49 +0100
> To: sdlnews#sdl-forum.org
> Subject: SDL-news: A question about history in SDL-2000
>
> Dear SDL users,
>
> I have a questions about the concept of history in SDL 2000.
>
>> From Z.100 section 11.11.2 State aggregation
> * An input transition associated with a composite state application
> containing a State-aggregation-node applies to all states of all state
> partitions, and it implies a default termination of all these. If such a
> transition terminates with a Nextstate-node with HISTORY, all partitions
> re-enter into their respective substates.
>
>> From Z.100 section 11.12.2.1 Nextstate
> * A Nextstate-node with HISTORY represents a <history dash nextstate>:. If
> a transition is terminated by a <history dash nextstate>:, the <state>:
> must be a <composite state>:.
> * When a Nextstate-node with HISTORY is interpreted, the next state is the
> one in which the current transition was activated. If interpretation
> re-enters a composite state, its entry procedure is invoked.
>
>
> First I lack the recommendation to describe what happens when a composite
> state that is not a state aggregation is re-entered through a nextstate
> with history. Does the description given for state aggregation also apply
> for any composite state?
>
> Assuming this, I would like to use history for describing the suspension
> and resumption of a composite state (and its substates). Suspension and
> resumption may be easliy described using "suspend", "resume" messages. When
> receiving a suspend message, a composite state would transit to a suspended
> state waiting for a resume message that would bring the state machine back
> to the composite state with history - i.e. with all substates in the same
> state as before suspension. It is not possible to describe suspension in
> that way using SDL 2000 because of the limitation set in 11.12.2.1 (see
> above): if history is used, the next state must be the state in which the
> transition is activated. I wonder why this limitation has been set by the
> study group 10? I lack support for re-entering a composite state with
> history at any time in a state graph.
>
> When re-entering a state, I found it difficult to deal with the entry
> procedure. I intended to describe initialisation actions in the entry
> procedure. Re-entering a state does not necessarily require the same
> initial actions to be performed as when entering a state. I lack a
> "re-entry" procedure or at least some basic support in SDL for testing the
> type of entry in a state (i.e. enter vs. re-enter). I wonder if this has
> been discussed in the study group 10?
>
> Thank you in advance for feedback,
> Jacqueline Floch.
When can we expect to see this answer?
-- Rick Reed - rickreed#tseng.co.uk Tel:+44 1455 55 96 55 Fax:+44 1455 55 96 58 Mob.:+44 7970 50 96 50
This archive was generated by hypermail 2a23 : Mon May 05 2008 - 20:30:55 GMT