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

142 Concepts for the Integration of Specification and Design
and three Instance Structure Diagrams A, B and C. Model A shows an outer system
boundary consisting of two clusters marked as distribution boundaries. These distribution
boundaries reflect the structure of the architecture. Notice that the architecture
prescribes one channel between the distribution boundaries. This situation is achieved
in diagram C. Figure 5.13 shows diagram B as intermediate model. A lot of Behaviour
Preserving Transformations are necessary to perform the transformation of diagram A
into C via B, because they are defined as very fine grain operations. See Chapter 10 for
a detailed description.
5.9.3 Transformation of Hierarchical Levels
Transformations enable addition and removal of clusters. We defined the concepts of
horizontal refinement, and of composition and decomposition refinement in Subsection
5.7.3. It appears that addition or removal of a cluster can lead to horizontal and vertical
modifications simultaneously. Figure 5.14 and Figure 5.15 show two models. Figure
Level
1
Level
2
Level
3
Figure 5.14: Hierarchical Levels 1
5.14 has two clusters on level 2. Removal of a cluster leads to the model in Figure 5.15.
Notice that the contents of the removed cluster move up one level. This example shows
that a modification on level 2 affect level 3 also. It shows that objects and clusters may
be defined during a refinement on a specific level, but that they may move afterwards.
When Figure 5.15 is considered as starting point, two entities are clustered on level 2.
The result has been shown in Figure 5.14. The entities that have been clustered fall