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

266 Process Part of POOSL
Sysp p
:: ¡ ¡ CD1 CDp k
Each Sys p is a system of process and cluster classes. It is built from a number of class
definitions. The collection of all class definitions ClassDef p ranges over CD p ¥¡ ¡ ¡ and is
defined as
CDp :: process class Cp yr ¥¡ ¡ ¡ ¥
¡ ¡
¡ ¡
y1
instance variables x1 xn
communication channels ch1 chk
message interface la 1 ¡ ¡ la ¡ ¡ ¥ ¥¡ initial method call
m
m(E1 Eq)()
instance methods MD p
1
¡ ¡ MDp
k
¡ cluster class Cc ¡ ¥ Pr ¥¡ ¡
¡ ¡
P1
communication channels ch1 chk
message interface la 1 ¡ ¡ la behaviour specification
m
BSpecp Within a class definition the functionality of the instances of the class is specified. We
distinguish two kinds of classes, each with its own specification format. The first kind
of class is called process class and the second kind is called cluster class.
A specification of a process class starts with the name of that class together with a
number of instance variables between angle brackets. Then the collection of all instance
variables of the process class is specified. These variables model the private or internal
data of each instance of the class. Upon initialisation of an instance of the class, the
instance variables specified between angle brackets are bound to a set of externally
supplied data objects. All the other instance variables are initialised to nil. Next, all
communication channels, through which the class’ instances communicate with other
processes, are specified. This channel specification is followed by a description of a
message interface. A message interface is a list of abstract send or receive actions, also
called abstract communication actions. Such an action states that a process can send a
certain message to a certain channel, or that a process can receive a certain message from
a certain channel. The set a of all abstract communication actions, has typical elements
l a ¥¡ ¡ ¡ and is defined as
l a :: ch!m§ n
ch?m§ n ¡
The first clause states that a process or cluster, at some point in time, can send message
m, together with n data objects, to channel ch. The second, complementary, abstract
action states that message m, with n data objects can be received from channel ch. n
denotes the direct naming of natural number n. The actions are called abstract because
they contain no information about the precise transferred data objects; only the amount
of objects is indicated. A message interface serves as an abstract description, often called
a signature, of the functionality of the instances of a process class.
The description of a message interface is followed by the specification of an initial method