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

362 SHE Framework
Service_
Scheduler
Feeder_Station
Feeder_Controller
Product_
Product_
pipo
Product_
i Input_
pihp
Info_
Output_
o
Handler
Keeper
Handler
piti
wake
Transporter_
Image
Transporter
pihs
wake
prks
Feeding_Unit_
fuis fesa
Image
titr fufu
poti
Feeding_
Unit
poss
pisa
Service_
Administrator
DISTR
Figure 11.18: Feeder Station: Instance Structure Diagram
topologies require special attention. They lead in general to mapping of many flows
onto one channel. This can have consequences for the behaviour description of the
process classes. Behaviour-Preserving Transformations can be used to transform channel
structures without affecting the system’s behaviour provided that the conditions for the
transformation are fulfilled.
Besides the formalisation of a system level structure that can be designed in Architecture
Structure Diagrams lower level design activities concern the more detailed internal
structure of a system. Figure 11.18 shows for instance a channel wake that connects
the processes Product Input Handler, Feeding Unit Image and Product Output Handler to
a process Transporter Image. In the next chapter, from which Figure 11.18 is borrowed, it
will become clear that low level channel design has implications for the formal behaviour
description of a system. Reusability is strongly influenced by how generic a class can be
designed. By sharing a channel a number of collaborating objects can do requests for a
service to an instance. Notice that the number of objects that can be connected this way
can be flexible. In contrast, pair-wise connections require dedicated connections and
make the message interface of the shared object dependent on the number of service