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

98 Abstraction of a Problem Domain
Servant A
Supervisor 2
Cluster Y
Servant B
Supervisor 1
Cluster X
Servant G
Supervisor 3
Cluster Z
Servant H
Figure 4.25: Hierarchically Supervised Composites
(For a further discussion of inner name and outer name, see Section 10.2).
The concept of channel hiding will be used in the behaviour description of clusters
and collaborating objects in general. The symbol denotes channel hiding. When the
behaviour of the classes of objects A, B, and C is specified in class definitions ClassOfA,
ClassOfB, and ClassOfC respectively, then the expression
b¥ c¦¨§ z© y a¥
describes the behaviour of the (clustered) composite. Its behaviour is the behaviour of
the parallel composition of internal objects A, B, and C, with channels a, b, and c hidden,
and with channel y renamed to z. ClassOfA(’A’) denotes that an object with identifier
(ClassOfA(¡ A¡ ) ¢ ClassOfB(¡ B¡ ) ¢ ClassOfC(¡ C¡ )) ¤£
’A’ is instantiated from class ClassOfA. The clause £
channels a, b, and c. The clause § z© y denotes the renaming of channel y to z (see Section
10.2 for details).
4.10 Terminators and System Boundary
a¥ b¥ c¦ denotes the hiding of the
So far we focused on objects that are internal with respect to the system boundary. Composites
in a reactive system can be used to perform a complex control task. A part of the
composite may be an image of a ’part’ outside the system boundary. Object C in Figure
4.27, for instance, is part of a clustered aggregate, and represents Sensor 1. This sensor
is outside the system and its image in the system is object C. This object is responsible