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Chapter 8. openETCS Domain Framework
changed by code generators if a statically typed programming language [79], as C++, is used.
Nevertheless, the behaviour depends heavily on the instantiation of objects, which means here
on the generated code and accordingly on the openETCS model. The consequence is that this
section can only show examples of models and their corresponding generated code by UML
diagrams for clarification.
Data Flow Example The data flow model in Figure 8.7 is used as example to describe the
corresponding behaviour, which is explained as follows. This example is very similar to the one
Value
double
0
double
double
(CONST) + >
double
1
(CONST)
Step 1
(CONST)
double
bool
Start->Running
Figure 8.7.: Example of a gSubFunctionBlock graph with a simple data flow
in Figure 7.15 that was used for the description of the mathematical model of the dynamic
semantics in Section 7.7. It is only extended about three objects on the right side. Those
and the new data flows between them add the following functionality: If the incremented
oVariableStorage object “Value” (initial value 0) is greater than 1, the oStateGuard object,
“Start→Running” is activated. Furthermore, Figure 8.7 should be a decomposition of the
“Starting” state in Figure 7.16.
Figure 8.8 introduces a UML interaction diagram [64] for two execution cycles (k = 0, 1) of
the example mapped / transformed to the domain framework. According to the description in
Subsection 8.3.1, all model objects are transformed to class instances of the openETCS domain
framework. Those are referenced by the m_FunctionBlocks aggregation of the CDataFlow
instance “DataFlow”. Due to the fact that an oStateGuard respectively CCondition object is
used, “DataFlow” is part of the CControlFlow “Parent” (Figure 7.16). Figure 8.8 introduces the
corresponding UML interaction diagram [64] for two execution cycles. Both execution steps k
are started by the Execute() message from the “Parent” control flow object to its CDataFlow
instance. To be precise, the control flow object must be a part of a superior CDataFlow object
that itself is part of a CEVCState instance starting the execution chain. For simplification
reasons, this is omitted in Figure 8.8. Neither, the CState object owning “DataFlow” is not
relevant for understanding the data flow behaviour and is omitted, too.
After the first Execute() message “Value” holds the value 0, “Sum” has the output 1 and the
“Greater” operator false. During the second Execute() message the output of “Sum” reaches
2, which causes that the “Greater” output switches to true and, as a consequence, triggers
the “Start->Running” condition. The triggered condition locates the related CTransition
object (not in the diagram) pRelatedTransition and places it on the the transition stack
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