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

140 Concepts for the Integration of Specification and Design
[vR92, Bor93]. A glass box is a module that can be modified internally. This requires
knowledge about its internal structure and behaviour.
The concepts of black, white, and of glass are used in the context of frameworks that are
described in the next paragraph.
5.8.3.5 Frameworks
All analysis boils down to the drawing of boundaries! The value of a well structured
model is high. A model has its value for understandability, implementation, documentation,
maintenance, test, redesign, subsequent design, etcetera. Reuse of designs can
be improved by giving additional attention to the internal structure (framework) of a
model. A framework is a generic object-oriented model (may be from specification to
code) for a specific class of applications. A framework is designed to offer a maximum
of reusable components and should require a minimum of changes to create an
application. It is a generic structure of collaborating instances of classes, that can be
transformed into a working application with a minimum modification effort. (Notice
that there are two completely different concepts of ’framework’. Outside this paragraph
’framework’ means ’method framework’ as has been defined in Section 4.1 and Subsection
5.4.2). Johnson’s [Joh94] research on frameworks emphasises the crucial value
of well structured systems. He refers to Peter Deutsch [Deu89], stating that: ’Interface
design and functional factoring constitute the key intellectual content of software and is far
more difficult to create or re-create than code.’ Information represented by clusters, that
are collections of collaborating clusters of objects, is a valuable intellectual result. This
cite confirms the difficulty of drawing such subsystem boundaries. Boundaries improve
structure modelling beyond the limits of traditional object-oriented modelling.
5.9 Transformations
5.9.1 Definition
A transformation is a modification of a model. It leads to a change of some properties of
the model (system), while others remain unmodified. Modelling consists of performing
a large number of transformations.
Horizontal refinement is achieved by adding objects, clusters, channels and messages
on a specific abstraction level. Composition refinement is achieved by adding clusters,
and decomposition fills a cluster with clusters and/or objects. Additions change the
structure of the model. Both the hierarchical and the channel structure are involved.
Boundaries specify properties of clusters. In general, boundaries are found from design
decisions documented in Architecture and Implementation Structure Models. In
general, boundaries are represented as clusters in Object Instance Models. Definition of
boundaries can lead to the need for additional clusters.