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DESIGN OF STATE DIAGRAM FACILITIES IN SCED
9
Figure 7. A state diagram in which each state has as many actions
as possible
and
(action2,default)
(action3, default)
(action4, null)
Let's consider a situation where the second event trace is synthesized after the rst
one. The synthesis of the rst event trace would gather actions \action1", \action3"
and \action4" into a single state. While synthesizing the second event trace, the
algorithm should notice that the maximal common path is:
(action3, default)
(action4, null).
Since we require that each state may have only either an automatic transition or
labeled transition as a leaving transition but not both, two states with several
actions can be joined only if both of them have same last actions (in the same
order). These last common actions will be placed into a single state (and perhaps
some actions will be removed from already existing states).
Gathering as many actions as possible into a single state prevents the algorithm
from forming automatic self-transitions, or more generally endless loops caused by
automatic transitions. That will be the case if there are two similar leaving events
or action boxes in a scenario without any arriving event between them. This is
illustrated in gures 8 and 9. Both of these state diagrams could be synthesized
from the following two event traces.
(actions2, event1)
(action1, default)
(action1, null)
(actions2, event2)
(action3, default)
(action4, default)
(action3, null)
Note that when a state has several actions, these actions are executed in succession. In OMT notation, however, actions associated with the keyword \do" are
executed simultaneously (or independently) and the actions executed in succession
are separated with a semicolon.
4.1.4. Names of transitions and actions. The names of transitions and actions in a
state diagram are directly the names of events attached to an object in a scenario
[13, 11]. To simplify the presentation the specications of receiver and sender objects
have been ignored. This is due to an assumption that the event names uniquely