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

138 Concepts for the Integration of Specification and Design
x
x Object A y z
u u a b
Design
decision
u
Object C
c
Cluster
Object B
Cluster used as concurrency boundary
(prescribes that the inside behaviour
must be sequential)
x
SEQ
Figure 5.12: Concurrency Boundary Notation
be a problem. Behaviour preserving transformations support structure changes at any
time. Behaviour modelling will become more clear in Chapter 6 where the concepts for
modelling dynamic behaviour are described. Further research should reveal heuristics
for the mapping of POOSL on various implementation description techniques, such as
VHDL, C, C++ and ABEL. Guidelines for using the power of POOSL in a restricted way
may improve efficiency of a mapping. Possible automation will also require in depth
knowledge of mapping processes.
5.8.3.2 Intersecting and Coinciding Boundaries
Boundaries are represented as objects or clusters. Therefore they cannot intersect. Boundaries
that do not intersect lead to simple models. Prohibiting intersection is a good
heuristic to diminish complexity of models. Abstraction boundaries map on clusters
so they cannot intersect each other. In general they encompass other boundaries, because
they are used for hierarchical structuring of the system model. Implementation
boundaries seem to represent an orthogonal concept. By mapping them onto clusters,
however, they cannot intersect each other. If boundary mapping requires new clusters
that appear to intersect, the model must be redesigned. Clusters must be decomposed
until they do not intersect anymore.
A process object is implicitly the smallest concurrency boundary. Its internal behaviour
is by definition sequential. Explicitly specified concurrency boundaries are always
mapped on clusters. The same holds for distribution boundaries. Both concurrency
boundaries and distribution boundaries cannot intersect because they are deliberately
defined on clusters.
z