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

12.4 Towards an Extended Specification 397
Instance variable positionNumber implements a coding of the actual position. To access
and transform the positionNumber two methods are defined:
instance methods
positionNumber:Integer
positionNumber
setPositionNumberTo(i:Integer):Position
positionNumber:=i;self
Notice that these methods are not specified in the Object Class Diagram of Figure 12.9.
The reason is that these methods are not considered essential. They are only used to
express the methods that are listed in the diagram of Figure 12.9. These methods are
specified as follows:
setToZero:Position
self setPositionNumberTo(0);self
increment:Position
positionNumber:=positionNumber+1;self
+(d:PositionDelta):Position
new (Position) setPositionNumberTo(self positionNumber + d deltaNumber)
-(p:Position):PositionDelta
new (PositionDelta) setDeltaNumberTo(self positionNumber - p positionNumber);
=(p:Position):Boolean
(p positionNumber) = (self positionNumber)
asInitialPosition:InitialPosition
new (InitialPosition) setPositionNumberTo(self positionNumber)
The last method is used to create an InitialPosition that is equivalent to the receiver of
the asInitialPosition object.
12.4 Towards an Extended Specification
The current generation of mailing machines is build upon a centralised control concept.
The initial requirements of the new generation of mailing machines state that these
machines should be build from plug-and-play stations all equipped with their own
intelligence. This requirement was at the basis of the essential specification we presented
in the previous section. The essential specification is still too abstract to be implemented
directly. First it has to be refined into an extended specification by adding implementationoriented
architecture and behaviour elements.