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

5.8 Boundaries 133
5.8 Boundaries
5.8.1 Introduction
In Chapter 4 we introduced objects and clusters as means to encompass functionality and
data, and as the entities for building models. It has been shown that objects and clusters
can form composites (subsystems). In this chapter we elaborate on the importance of
structures and its formalisation into a behaviour model. The various sorts of structures
show conceptual, spatial and temporal decomposition of a (sub-)system. They can
specify various properties of subsystems, which must be reflected in the style of the
behaviour description. We introduce various sorts of boundaries as means to define
various forms of structure explicitly.
5.8.2 Definitions
A boundary is an enclosing of modelling entities. A boundary may be represented
graphically in a diagram as a (closed) curve, or may be added as a property to a composite
of modelling entities. Its purpose is the definition of a property of a composite or an
object. Such an entity may have the property to be:
a nameable part of the problem domain;
an abstraction;
prescribed to be implemented by a specified technology;
a concurrent module;
a part of a distributed structure.
According to these properties we define corresponding sorts of boundaries in the next
paragraphs. These boundaries are
domain boundaries;
abstraction boundaries;
implementation boundaries;
concurrency boundaries;
distribution boundaries.
5.8.2.1 Domain Boundary
A domain boundary is an enclosing that represents a nameable part or entity of the problem
domain. In a description of a problem domain various entities can exist. Entities are
specified into Object Instance Models as objects or clusters. Composites are composed
into larger composites in the higher levels of a complex model. All composites are
represented by clusters. All objects and clusters are Domain boundaries. They enclose