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

12.3 The Essential Specification 389
PositionDelta 16 . A Position can be setToZero and can be incremented. Further a PositionDelta
can be added to it, or a Position can be subtracted from it. If a Position is sent the message
asInitialPosition it will create a new and equivalent InitialPosition object. The data class
InitialPosition is a specialisation of data class Position.
12.3.8 The POOSL formalisation
When Message Flow Diagrams, Instance Structure Diagrams and Object Class Diagrams
are ready, the model can be formalised in the POOSL language. For the formalisation of
the complete control system we consider the Instance Structure Diagram of Figure 12.7.
From this diagram it easily follows that the specification is of the form:
( Station§ i1© i¥ c1© o
Feeder
Merger Station§ c1© i¥ c2© o¥ c6© si
¢
¢ Feeder Station§ c2© i¥ c3© o
¢ Packer Station§ c3© i¥ c4© o
¢ Separator© Printer Station§ c4© i¥ c5© o
¢ Stacker Station§ c5© i¥ o1© o
¢ Feeder Station§ c7© i¥ c6© o
¢ Feeder Station§ i2© i¥ c7© o
¢ Product Information Server
) £
c1¥ c2¥ c3¥ c4¥ c5¥ c6¥ c7¥ i1¥ i2¥ o1¦
Each of the stations is an instance of a corresponding cluster class. The feeder stations
are instances of cluster class Feeder Station. From Figure 12.8 it follows that the instances
of this class are built from a Feeder Controller instance, a Transporter instance and from a
Feeding Unit instance. The specification of the Feeder Station class is as follows:
cluster class
§©¨£¨
¢¡£¡£¤¥¡£¦
"Cluster type: module of distribution."
communication channels
i o
message interface
i?accept(PI)
o!accept(PI)
behaviour specification
( Feeder Controller
Transporter
Feeding Unit
)
The Feeder Controller is a cluster that is built from a Product Input Handler, a
number of Product Info Keepers, a Product Output Handler, a Service Scheduler, a
Service Administrator, a Transporter Image and a Feeding Unit Image, see Figure 12.8.
16 The PositionDelta is the unity of difference. ’Difference’ is the gerund of ’to differ’. The gerund, indicated
by the symbol, means that a relation is modelled as an object.