Ph.D. - geht es zur Homepage der Informatik des Fachbereiches 3 ...

8.4. Behavioural Design
execution (see Figure 8.7) of “Starting” finally activates the “Start->Running” condition, which
causes in Figure 8.9 that the reference of the related CTransition “TransSleepingRunning” is
placed on the m_TransitionStack of “Parent” by the push_back() message. After the parent
control flow noticed that the transition stack is not empty (result of size), it gets the priority
by GetPriority() and the reference to the target state by GetTargetState(). The priority
is used to determine, which new state is switched to in the case if the stack would hold more
than one transition object. Finally, in the current execution step “Parent” sets internally its
m_pCurrentState aggregation to the reference of “Running”. Therefore, in the next execution
step “Parent” sends the Execute() to “Running” to execute its data flow and so on.
EVC State Machine Example Although the EVC state machine graph type gEVCStateMachine
also defines a control flow, it differs a little bit from the gEmbeddedStateMachine graph
type in the behaviour because it describes two nested state machines. The superior one is for
the EVC Modes (CEVCState class) while the switching of ETCS Application Levels is nested
within. Because the switching of the Application Level only means a context switch of the
current CEVCState object m_pCurrentState, the levels are simply distinguished by a string
stored in m_CurrentApplicationLevel. A certain class for Application Level switching, like
CTransition, is accordingly not required because the condition objects of class CLevelCondition,
which corresponds to oApplicationLevelType in the meta model, can directly write their level
in the parent CEVCCondition object if they are activated by a Boolean data flow.
Thus, the preceding example for a control flow does not cover this speciality, and an
additional example for an EVC is discussed. Figure 8.10 represents the transition matrix (of an
gEVCStateMachine graph) of a strongly simplified EVC state machine. It only consists of the
Starting (INITIAL)
Running
Starting (INITIAL) Running
c1-p0
Figure 8.10.: Transition matrix for an simple EVC example
states “Starting”, which is the initial one, and “Running”. From “Starting” to “Running” exists
exact one transition under the condition “c1” with the priority 0. It is obvious that this example
does not correspond to any Modes or parts of the ETCS SRS and is only used to exemplary
demonstrate the behavioural design of the EVC state machine. “Running” is available in
Application Level 0 and 1, which means the oEVCState object must have two explosions: One
for each Level. Figure 8.11 shows the gMainFunctionBlock graph for Application Level 0 and
Figure 8.12 for Level 1. “Running” is only available in Application Level 1, but its explosion
is not relevant for this example and accordingly omitted.
Both data flows of “Starting” use the already introduced and described counter construct. In
Level 0, after one calculation step, the oApplicationLevelType object for Level 1 is activated
by a true Boolean data flow, which means a context switch to Level 1 is then initiated. In
Level 1, the counter has the limit 2. If it is reached, the condition “c1” is activated, with means
a transition to the state “Running”. The UML interaction diagram with the primary objects
137