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

6.6 Dynamic Behaviour 211
6.6.5 Modelling Behaviour of Data Objects
Traditionally an object is a collection of operations that share a variables state. The
operations determine the messages to which the object can respond. The variables
state is hidden from the outside world and is accessible only to the object’s exported
operations. Variables representing the internal variables state of the object are called
instance variables and its operations are called methods. The collection of methods
determines an object’s interface and its behaviour.
Data objects (in contrast to process objects) follow a traditional object-oriented approach.
A precise description of the syntax and semantics of data objects can be found in Chapter
8. In this subsection we give an informal description of how dynamic behaviour of data
objects is modelled.
6.6.5.1 Data Class Specification
The behaviour of a data object is described in its class. A data class definition begins
typically as:
data class C
instance variables x1 : C1 ¡ ¡ xn : Cn
instance methods MD1 ¡ ¡ MDk
The keyword data class announces the declaration of the class name denoted as C here.
Next follows a declaration of the instance variables. They model the attributes. Each
instance variable is assigned a type in the form of a data class. The instance methods
specify the possible forms of behaviour. The instance method names define the message
names that the object can respond to. In contrast to process objects there is no explicit
description of the message interface.
A method definition MD is of the form:
m(u1 : C1 ¥¡ ¡ ¡ ¥ un : Cn) ¡ v1 : C¡1 ¥¡ ¡ ¡ ¥ vn : C¡2 ¡ E
or of the form:
m(u1 : C1 ¥¡ ¡ ¡ ¥ un : Cn) primitive
The behaviour of a method is normally described in a user defined data expression E. An
alternative form of behaviour is a so-called primitive method which is not user defined.
Primitive methods are pre-defined built-in methods.
A method is specified with one or more parameters ¢
the objects that are contained in a message that requires the execution of this method.
Each parameter is assigned a type in the form of a data class.
u1¥¡ ¡ ¡ ¥ un £ . The parameters represent
Further there can be specified zero or more local variables ¡ v1¥¡ ¡ ¡ ¥ vn ¡ . They are for
temporary storage of intermediate results of internal calculations. They do not represent