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

5.9 Transformations 141
The modification of the clustering over various abstraction levels appears to be an
important type of transformation. In comparison to modifications of process objects,
modifications of clusters have a weak influence on the system behaviour. This observation
enabled the definition of a set of behaviour-preserving transformations on clusters.
They are described in Chapter 10. In general, the word transformation means behaviourpreserving
transformation in this thesis.
5.9.2 Purpose of Transformations
Transformations enable addition and removal of clusters as well as channels, while preserving
behaviour. They indirectly enable the formalisation of boundaries into a model,
because they can modify clusters. Transformations help to make an Object Instance
Model consistent with an Architecture or Implementation Structure Model. Especially
the modification of channels is important. Initially, channels are defined more or less
’automatically’. If two process objects exchange a message, they need at least one channel.
If process objects exchange several types of messages they are in principle mapped
onto one channel. Adding a second channel, or sharing a channel must be designed
explicitly. It is a deviation of the ’automatic channel approach’. Shared channel structures
such as backbones, star or ring topologies are typically designed in architecture
and implementation structures. Figure 5.13 shows an Architecture Structure Diagram
A
DISTR DISTR
B
Architecture Structure Model
( Distibuted topology)
DISTR DISTR DISTR
DISTR
Figure 5.13: Distribution Transformation
C