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

5.10 Formalisation 143
Level
1
Level
2
Level
3
Figure 5.15: Hierarchical Levels 2
to level 3. Addition of a cluster on level 1, can be considered a horizontal refinement.
This transformation causes also changes on level 3. There appear to be entanglements
of the various forms of refinement. Both removal and addition affects the next lower
level. This is only a simple example. In a hierarchy with more levels, more levels will
be affected. The complete hierarchical tree of clusters and objects in the cluster to be
removed or added will move. All these transformations are supported as behaviour
preserving transformations, that are proven correct.
5.10 Formalisation
This chapter paid a lot of attention to hierarchical structuring, and structure transformations.
However, the properties, that are prescribed by the definition of boundaries,
must also affect the behaviour description of process objects. Figure 5.16 visualises the
effort that must be done. After a thorough analysis, using mainly graphical representations,
a POOSL description of all classes must be written. This description integrates
many properties of the overall model into a formal Unified Model. On the one hand the
derivation of this model must be postponed until the graphical models become stable
and mature, on the other hand POOSL exercises give a lot of insight. Postponement
can prevent costly iterations of POOSL descriptions. However missing the insight that
comes with modelling attempts may cause iterations. Adequate guidelines must be
derived from future specification projects. In practice, it appears that there are many