Subject: RE: SDL-News: A question about history in SDL-2000
From: Birger Møller-Pedersen (ETO) (Birger.Moller-Pedersen#eto.ericsson.se)
Date: Mon Feb 25 2002 - 14:26:25 GMT
As far as I recall the restriction on history was introduced at a stage where we transformed to SDL without composite states. I am not sure if this transformation is still important, but if not, then there should be no problem in removing this restriction.
/birger
> -----Original Message-----
> From: Eckhardt Holz [mailto:holz#informatik.hu-berlin.de]
> Sent: 20. desember 2001 17:00
> To: Rick Reed TSE
> Cc: Birger Møller-Pedersen; meeting
> Subject: Re: SDL-news: A question about history in SDL-2000
>
>
> Dear all,
>
> after checking my memory and some files on my computer I`ll give some
> short answers here:
>
>
> On 12/19/2001 4:36 PM, Rick Reed TSE wrote:
>
> > 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
> (...)
>
>
>
> >>
> >>
> >> 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?
> >>
>
>
> Yes, a nextstate with a history applies to any composite
> state. It has a
> deep history semantics, i.e. the innermost state(s) where the
> transition
> did originate will be the target of the nextstate.
> Dash-nextstate on the other side is a shallow history, i.e.
> the target
> is the (composite) state where the input-part of transition
> is directly
> attached to.
>
>
> >> 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.
>
>
> We have discussed this issue at least by e-mail (cf. mails concerning
> TDA13 Item 18, Oslo(?)-Meeting), but decided to be consistent
> with the
> existing dash-nextstate. It is therefore not possible to
> suspend, go to
> some other state and later resume.
> Anyway - I will think about the suspend-resume-issue it
> little bit more,
> may be there is some other solution.
>
>
> >>
> >> 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?
>
>
> Here SDL follows the same path as UML, if you enter some
> internal state,
> you have to perform all the exits and entries along your way. History
> remembers the last state of the statemachine (where you left it), not
> the state of your local data (variables etc.)
>
>
> >>
> >> 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
> >
>
> I wish you all a merry christmas & happy new year
>
> Eckhardt Holz
>
>
> >
>
>
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