Subject: SDL-News: A question about history in SDL-2000
From: Jacqueline Floch (Jacqueline.Floch#item.ntnu.no)
Date: Tue Nov 06 2001 - 15:06:49 GMT
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-----From Jacqueline Floch <Jacqueline.Floch#item.ntnu.no> to sdlnews -----
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.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ jacqueline.floch#item.ntnu.no ~~~
Jacqueline Floch Tel: +47 73 59 30 12
ITEM, NTNU Fax: 73 59 44 66
N-7491 Trondheim, Norway Priv: 73 51 52 77
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ http://www.item.ntnu.no/~jacf ~~~
--End text from Jacqueline Floch <Jacqueline.Floch#item.ntnu.no> to sdlnews ---
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