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

6.6 Dynamic Behaviour 213
to pay attention to OMTs steps for constructing a class model, the rules for keeping the
right classes and the rules for keeping the right associations.
6.6.5.3 Data Object State
Conform the definition of behaviour state for process objects, we interpret this concept
for data objects now. Before a data object can come in a state it must be created. A data
object is either idle or it is executing a method. The state Idle means that the object is
waiting for a message that will start the execution of a method. When a data object is
executing a method this can be considered as a behaviour state.
6.6.6 Modelling Behaviour of Process Objects
In contrast of data objects that follow the object-oriented tradition, process objects offer
an additional modelling power needed for complex reactive hardware/software systems.
Process objects offer non-determinism, asynchronous parallel collaboration, sequential
internal behaviour, infinite behaviour, synchronous communication, and static
interconnections. Many of these properties have been discussed already. In this subsection
we give an informal description of some aspects of internal behaviour descriptions
of process objects. A precise description of the syntax and semantics of process objects
can be found in Chapter 9.
6.6.6.1 Process Class Specification
The behaviour of a process object is described in its class. It is described by a collection
of instance variables and a collection of instance methods. In contrast to data objects,
process objects also need the specification of communication channels, of a message
interface and of an initial method call. A process class definition is typically of the form:
process class C p y1 ¥¡ ¡ ¡ ¥ yr ¡
instance variables x1 : C1 ¡ ¡ xn : Cn
communication channels ch1 ¡ ¡ chk
message interface l p
1 ¡ ¡ lp m
initial method call m(E1 ¥¡ ¡ ¡ ¥ Eq)( )
instance methods MD p
1
¡ ¡ MDp
k
¥¡ ¡ ¡ ¥ ¡ ¥¡ ¡ ¡ ¥
¥¡ ¡ ¡ ¥ ¡
The first element is the declaration of the process class name C with a list of instance
variables y1 yr . This list is the subset of the instance variables x1 xn. The
list y1 yr contains the variables that will be initialised upon instantiation of
the system. In contrast to data objects that are created on run-time, process objects are
created at ’compile-time’. A system model contains a finite stock of process objects
connected by channels when it starts running.
The possible communications of a process is determined by its message interface l p
1 ¡ ¡ lp m.
The message interface is a list of elements l p . The elements l p have typically the form
ch!m(C1 ¥¡ ¡ ¡ ¥ Cn) or ch?m(C1 ¥¡ ¡ ¡ ¥ Cn) denoting that messages can be sent or received on
channel ch. C1 ¥¡ ¡ ¡ ¥ Cn denote the types of data objects that are transported with the
message.