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

9.3 Formal Syntax 267
call of the form m(E1 ¥¡ ¡ ¡ ¥ Eq)(). After initialising its instance variables, a process object
always starts its activities by calling its initial method. This method does not contain
any output parameters.
The last part of a process class definition consists of a number of method definitions. A
method definition specifies the behaviour of its corresponding method. The set MethDef p
of all method definitions, with typical elements MD p ¥¡ ¡ ¡ , is defined as
MD p :: m(u1¥¡ ¡ ¡ ¥ um)(v1 ¥¡ ¡ ¡ ¥ vn)
¡ w1 ¡ ¡ wk ¡ S p
A method definition contains a header with name m, input parameters u1¥¡ ¡ ¡ ¥ um and
output parameters v1¥¡ ¡ ¡ ¥ vn. The method header is followed by a declaration ¡ w1 ¡ ¡ wk ¡
of local variables. Then the message body, which is a statement S p , is defined. Method m is
invoked through an m(E1 ¥¡ ¡ ¡ ¥ Em)(p1¥¡ ¡ ¡ ¥ pn) statement. Such a statement is executed by
first evaluating E1 ¥¡ ¡ ¡ ¥ Em from left to right and by binding the results to input parameters
u1 ¥¡ ¡ ¡ ¥ um. The output parameters v1 ¥¡ ¡ ¡ ¥ vn and local variables w1 ¥¡ ¡ ¡ ¥ wk are initialised
to nil. Then statement S p is executed. If this statement terminates successfully, the
output parameters v1 ¥¡ ¡ ¡ ¥ vn are bound to variables p1 ¥¡ ¡ ¡ ¥ pn and the method execution
terminates.
The second kind of classes are called cluster classes. A cluster class is built from other
classes, which are either process classes or cluster classes themselves. A class definition
of a cluster class consists of a cluster class name with a number of expression parameters
P1 ¥¡ ¡ ¡ ¥ Pr between angle brackets, a number of communication channels, and a message
interface. The behaviour of a cluster class is specified by means of a parameterised behaviour
specification. The set BSpecifications p of all parameterised behaviour specifications
has typical elements BSpec p and is defined as follows:
BSpec p :: C p (PE1 ¥¡ ¡ ¡ ¥ PEr)
¡ C c (PE1 ¥¡ ¡ ¡ ¥ PEr)
BSpec ¡ p
¡
1
BSpecp BSpecp2
¢
L
BSpec ¡ p f §
Here each PEi denotes a parameterised data expression. The set of all parameterised data
expressions is ParExp and ranges PE¥¡ ¡ ¡ over . ParExp is defined as
PE :: P
E ¡
PE m(PE1 ¥¡ ¡ ¡ ¥ PEn) ¡
PS;PE
¡