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

218 Modelling of Concurrent Reactive Behaviour
a cluster contains the parallel composition of objects and clusters which is denoted by
BSpec p
1
¢ BSpecp
2 .
One of the purposes of a cluster can be the explicit hiding of internal communication
(see Section 4.9). In general, not all channels are hidden. Some channels must cross the
cluster boundary for communication with the environment of the cluster. BSpecp L
denotes that the channels in L cannot be used for communication with the cluster’s
environment and are made unobservable for this environment. This is illustrated with
Figure 6.21. Cluster X can be used to hide Object A, Cluster B and Cluster C. The internal
communication channels d, e and f cannot be used by the environment of the cluster.
They are used for internal communication only. In contrast channels a, b and c cannot be
hidden because they are used for communication with the environment of the cluster.
If BspecX is the behaviour specification of cluster X then BspecX £
e¥ f ¦ denotes the
d¥
hiding of the internal channels d, e and f. At a lower level the same approach can be
used for clusters B and C. They have internal channels k, l, m and n that can be hidden.
a
a
Object A
e
i
d
i
l j
m n
Cluster C
Cluster X
l j
m n
Cluster B
Figure 6.21: Channel Renaming
k
k
b
f
b
c c
A behaviour specification of the form Bspec p § f denotes a channel renaming. A complex
system is usually constructed as a topology of channels that connect various clusters and
process objects. Processes and clusters are specified in classes. All instances of the same
class have in principle the same channel names determined by the message interface
of their class. If all instances are connected to a common channel there is probably no
need to rename this channel. Figure 6.22 shows an example. One of the clusters of the
multiple of clusters in Figure 6.22 can for example be as illustrated in Figure 6.21. The
inner names and the outer names of channels a, b and c are the same.
The necessity of renaming becomes clear when we look at clusters B and C in Figure
6.21. Both are instances of the same class. However both are hooked up in a different
way. Inner channel j of Cluster C is connected to Cluster B, while the channel j of Cluster