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

6.6 Dynamic Behaviour 215
A method definition MD p of a process class is typically of the form:
m(u1 : C1 ¥¡ ¡ ¡ ¥ um : Cm)(v1 : C¡1 ¡ ¡ vn : C¡n )
¡ w1 : C1" ¡ ¡ wk : Ck" ¡ S p
in which m is the method name, u1 ¥¡ ¡ ¡ ¥ um are input parameters, v1 ¥¡ ¡ ¡ ¥ vn are output
parameters, w1 ¡ ¡ wk are local variables and S p represents the statement(s) for the
behaviour operation.
6.6.6.5 Statements
POOSL enables an imperative programming style for specifying behaviour. A method
is typically composed from process statements of the form:
1 S
2 S p
1; S p
2
3 if E then S p
1
4 do E then S p od
5 S p
1
or Sp
2
else Sp
2 fi
6 § E S p
7 m(E1 ¥¡ ¡ ¡ ¥ En)(p1 ¥¡ ¡ ¡ ¥ pm)
8 ch!m(E1 ¥¡ ¡ ¡ ¥ En)
9 ch?m(p1 ¥¡ ¡ ¡ ¥ pm ¡ E)
10 S p
1
11 S p
1
abort Sp
2
interrupt Sp
2
1. A process statement can be a data statement S as described in the previous subsection.
2. Statement S p
1; S p
2 shows that a statement can be a sequential composition of statements.
3. There are various ways to create branching in the sequences of statements. The if
statement has its usual meaning.
4. The do statement has also the usual meaning, which is the same as the meaning of
a traditional while statement.
5. The choice statement S p
1 or S p
2 defines a non-deterministic selection. One of the
alternative behaviours S p
1 or S p
2 is chosen. Non-determinism11 is a powerful feature
for the description of abstract behaviour. It offers a mechanism for the description
of possible alternative forms of behaviour in an early phase of the system analysis.
Non-deterministic changes of behaviour typically happen in complex concurrent
systems. An or statement is appropriate to describe the selection of behaviour
11 In automaton theory non-determinism is the ability to change state in a way that is only partially
determined by a current state and an input symbol. It permits several possible next states for a given
combination of current state and input symbol [LEWI81].