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8.5. Deployment Design
According to the discussion about security problems caused by platform-specific adaptations
in Chapter 6, implicitly, only direct communication – in form of method calls – from the PIM
to the PSM is allowed to further minimise the possible, malicious influence of platform-specific
adaptations on the PIM. Hence, communication from the PSM to the PIM is only possible
through the D-Bus signalling mechanism [31], which avoids that the adaptors in the PSM have
any knowledge about connected proxies in the PIM.
In contrast to the interface classes, the adaptor classes cannot be used directly since the
messages and signals defined in the XML file must be implemented. This implementation
is an often recurring task because the implementation must be adapted for each (hardware)
interface even for simulative implementations for testing. Therefore, a stub class is provided
for each adaptor class, which methods only have to be extended by class inheritance and
overriding [79]. The stub classes are shown in Figure 8.18. Similar to the function block classes,
Figure 8.18.: UML class diagram of the adaptor stub classes
also the corresponding adaptor stubs, CBaliseDeviceIn, CBaliseDeviceOut, CEmergencyBrake,
CServiceBrake, and COdomoter inherit from QObject to be able to use the Qt 4 signal and
slot mechanism. The classes are located within the “PS” 10 package of the openETCS domain
framework package, which means in C++ in the ::oETCS::DF::PS name space. In contrast
to other middleware, like CORBA, adaptor implementations for the Qt 4 D-Bus API are not
done by inheritance from the adaptor classes but by an association of the generated adaptor to
a QObject that provides the implementation of the adaptor methods. Thus, these associations
are not sketched in Figure 8.18.
The UML deployment digram in Figure 8.14 only refers to two library components: One for
the platform independent and the other for the platform specific implementation. Of course,
10 abbreviation: platform specific
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