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

11.5 Extended Specification Modelling 371
object_1
(essential
model)
channel_ch
(essential
model)
Figure 11.19: An Abstract Channel
object_2
(essential
model)
implemented with the use of a protocol. This can imply complex behaviour. A simple
message passing in the essential model now becomes a procedure with a connection
phase, a transmission phase and a disconnection phase. Provisions must be taken when
messages are distorted and must be repeated, etcetera. Figure 11.20 shows how the
object_1
(essential
model)
object_a
(extended
model)
object_b
(extended
model)
Figure 11.20: Extended Channel Model
object_2
(essential
model)
channel in Figure 11.19 can be extended with object a and object b that implement the
protocol behaviour. Another approach is shown in Figure 11.21 where the channel is
modelled as an object. This can be a solution for the modelling of a shared channel as
an autonomous entity that decides what communication with what priorities can occur.
Figure 11.22 shows an approach where clustered objects from the essential model are
extended with object a and object b. Both clusters can for example require a different
implementation technology. Typical extensions of behaviour are modelled preferably
locally.
Besides the exploration of extensions the extended modelling phase is used to perform
mapping of processes on resources such as processors. Processes that are allocated to
one particular processor must be clustered. A system with more than one processor
can be modelled as a distributed system. The modules of distribution are modelled