Specification of Reactive Hardware/Software Systems - Electronic ...

370 SHE Framework
11.5.3 Implementation Structure Modelling
The starting point for extended implementation structure modelling is in general the
set of Architecture Structure Diagrams. These diagrams are refined and annotated with
textual information that shows implementation decisions explicitly. The implementation
technology for functional modules is annotated in the module symbols and the selected
communication technology such as protocols are denoted on channels.
The diagrams are not necessarily extended with new channels or modules. This is
because the purpose of Implementation Structure Diagrams is to specify the structure on
system level. After all, detailed implementation structures can be modelled in Extended
Instance Structure Diagrams.
Design decisions are motivated in an Implementation Decisions Statement that is integrated
in a Requirements Catalogue.
11.5.4 Extension of Message Flow Diagrams
The Message Flow Diagrams of a system are extended, based on the implementation
design decisions specified in Extended Implementation Structure Diagrams. Diagrams
are refined by inserting objects or by changing objects. This requires a multidisciplinary
point of view again. Aspects such as testability, maintenance and manufacturing can
lead to functions that could not be specified before the implementation decisions were
taken.
All existing essential scenarios are evaluated for the consequences of the various implementation
decisions. This can lead to a variety of new communications and corresponding
functions. Examples are:
imperfections of technology and the required reliability can lead to drastic changes
of the architecture of a system, such as a duplication of sub- modules;
addition of system interface modules that implement interface technology between
terminators and system;
detailed communication in user interfaces;
self test functions;
automatic call for maintenance functions;
functionality of communication protocols;
buffers, queues.
The extension of the models with new objects is illustrated in Figures 11.19 and 11.20.
Figure 11.19 shows a communication channel of an essential model. No decisions
have been taken about how this communication can be performed. When the essential
model is transformed to an extended model it may appear that the channel must be