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

144 Concepts for the Integration of Specification and Design
different styles and sorts of behaviour descriptions that match to specific needs.
Properties of entities (clusters or objects) can be determined by boundaries. Concurrency
boundaries require a sequential programming style. In contrast, concurrency
enables that entities take initiative simultaneously, and that they have responsibilities
for communication with various concurrent objects in the system environment. Implementation
boundaries may require the use of constructs that facilitates the mapping on
specific implementation description tools or languages. Domain boundaries can influence
the structuring of behaviour in general. Entities must encompass a recognisable
part of the problem domain, with a name according to problem domain vocabulary. Abstraction
boundaries affect the transparency of an entity. A cluster may be a transparent
domain boundary. Collaborating objects may know the identifiers of objects inside the
cluster. Such a cluster does not hide the internal objects. A cluster may be an aggregate.
Such a cluster is not transparent. All communication with the outside is handled by
one object inside the cluster. This object, with its identifier, represents the aggregate.
It will be clear that all these aspects affect the POOSL description heavily. The next
chapter describes more in detail what concepts can be used to model communication,
and dynamic behaviour.
5.11 Summary
The specification of complex reactive hardware/software systems is strongly affected
by various forms of structure. We described concepts and a framework to enable
simultaneous development of a behaviour and a structure model. Multidisciplinary
views will be addressed by scenarios. Important system properties are imposed by
boundaries. Structure is integrated in a unified model by transformations. A framework
guides the designer, gives awareness about places in the design space, and divides the
specification process into two major phases. Various properties of entities must be
realised in formal behaviour descriptions in POOSL. The concepts for this description
follow in the next chapter.