14.08.2013 Views

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

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

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

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!