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

12.5 Concluding Remarks 399
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DISTR
Feeder_
Controller
DISTR DISTR DISTR DISTR DISTR
Printer/
Merger_
Feeder_
Packer_
c1 c2 c3 c4 Separator_ c5
Controller
Controller
Controller
Controller
c6
Feeder_
Controller
c7
Feeder_
Controller
DISTR
DISTR
i2
Product_
Information_
Server
Figure 12.11: Instance Structure of Fully Distributed Control System
DISTR
Stacker_
Controller
distributed fashion 20 . The appearance of preconditions is a major advantage of the use of
the formal transformation system. For it automatically yields the explicit implementation
constraint stating that CAN must support weakly distributed communication. The
fact is that CAN indeed satisfies this constraint. A CAN network consists of modules
that are connected by one physical CAN bus. Each module in the network is identifiable
by a unique address. This knowledge leads to a refined Implementation Structure
Diagram as shown in Figure 12.13. The CAN modules implement a protocol for the
communication over the physical CAN bus. To get insight in whether CAN establishes
a useful communication medium, it is necessary to create models (objects) of the CAN
modules. This leads to an obvious extension of the Instance Structure Diagram of Figure
12.12.
12.5 Concluding Remarks
The model presented in this chapter is a very simplified version of the first welldeveloped
model of the Buhrs case. A number of previous models, iterations, modifications
and refinements were necessary before this model became more or less stable.
20 This is due to the transformation condition of transformation T6.
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