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

190 Modelling of Concurrent Reactive Behaviour
A
A knows B
A knows C
C
C knows A
Request to send
a result to B
request to B
answer to A
Distribution boundary, Module X
6.4.4.2 Strong Distribution
B
B knows A
K
K knows L
answer to K
request to L
Distribution Boundary, Module Y
Figure 6.15: Separate Name Spaces
L
L knows K
The notion of strong distribution is redefined based on the channel mechanism: A
system is strongly distributed if its modules (subsystems) communicate autistically 5 or
strongly distributed via static links. Figure 6.16 shows a distributed system. Distribution
A
Module X
request to B
answer to A
DISTR, HIDE
B
channel
Module Y
A
DISTR, HIDE
answer to A
request to B
Figure 6.16: Strongly Distributed Communication
boundaries cluster two subsystems X and Y. Both X and Y are so-called modules of
distribution. Recall that distribution boundaries denote physical distribution. This does
not prescribe a strongly distributed communication form. However a separation of
name spaces can be advantageous. It is a separate design decision to define the clusters
to be strongly distributed. Abstraction boundaries are used to denote this. See the HIDE
annotation in Figure 6.16. Notice that objects A and B in subsystem X can have dynamic
5 Recall that an autistic process object communicates solely without the use of identifiers of other objects,
autistic communication is communication on a channel without the use of identifiers of the participants.
B