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

4.5 Clusters 79
flows. Clusters enable hierarchy in system models. They allow nesting of clusters and
Object A Object B
Cluster C
Cluster X
Figure 4.16: Nested Clusters
objects into a hierarchy of granules. Figure 4.16 shows a nested cluster. Cluster C is
clustered together with Object A and Object B into Cluster X. Recall that process objects
Object A Object B
Cluster C
Cluster X
Figure 4.17: Clusters and Channels
are connected by channels. Every communication flow shown in Figure 4.16 requires a
channel. Figure 4.17 shows a number of channels that support the communication flows
defined in Figure 4.16. Notice that the three flows between object A and B are mapped
onto a single channel. This choice is arbitrary. We could also have chosen to map the
flows onto two or three separate channels.
The expressive power of clusters to visualise hierarchical structure and perform nesting
offers hardware designers the possibility to work as they are accustomed to. They tend
to use hierarchically nested block schemes extensively. Clusters can be used to support