Reactive Systems: Modelling, Specification and Verification - Cs.ioc.ee
Reactive Systems: Modelling, Specification and Verification - Cs.ioc.ee
Reactive Systems: Modelling, Specification and Verification - Cs.ioc.ee
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2.1. SOME CCS PROCESS CONSTRUCTIONS 15<br />
✬<br />
CM<br />
✫✉<br />
coin<br />
✬<br />
CM’<br />
✫✉<br />
coin<br />
✩<br />
coff<strong>ee</strong><br />
✉<br />
coff<strong>ee</strong><br />
✪<br />
✩<br />
✉<br />
coff<strong>ee</strong><br />
✪<br />
✬<br />
CS<br />
✉ ✉<br />
✫✉<br />
coin<br />
✩<br />
pub<br />
✪<br />
Figure 2.4: The interface for process CM | CS | CM ′<br />
As pictured in Figure 2.5, the restricted coin <strong>and</strong> coff<strong>ee</strong> ports may now only be<br />
used for communication betw<strong>ee</strong>n the computer scientist <strong>and</strong> the coff<strong>ee</strong> machine,<br />
<strong>and</strong> are not available for interaction with their environment. Their scope is restricted<br />
to the process SmUni. The only port of SmUni that is visible to its environment,<br />
e.g., to the competing computer scientist CS ′ , is the one via which the<br />
computer scientist CS outputs her publications. In general, the formation rule for<br />
restriction is as follows:<br />
If P is a process <strong>and</strong> L is a set of port names, then P \ L is a process.<br />
In P \ L, the scope of the port names in L is restricted to P —those port names can<br />
only be used for communication within P .<br />
Since a computer scientist cannot live on coff<strong>ee</strong> alone, it is beneficial for her<br />
to have access to other types of vending machines offering, say, chocolate, dried<br />
figs <strong>and</strong> crisps. The behaviour of these machines may be easily specified by means<br />
of minor variations on equation 2.1 on page 11. For instance, we may define the