5 Summary and conclusions
The object-oriented approach offers important
advantages over traditional software engineering approaches
for the development of communications software:
The design is simpler and clearer, and hence easier
to understand.
Re-usability can save time and effort [3], [5].
Changes and extensions can be easily incorporated
into the design, as the object-oriented approach
offers flexiility [2],[11].
The developed system is reliable and modifiable as
each object is independent from others.
The general framework we have developed provides
the basis for an object-oriented design. It defines
a number of abstract classes which capture common aspects
of the OS1 communication protocols. We have
tested and refined the general framework by prototyping
it in ObjectworkSmalltalk [28]. AU the abstract
classes and some example concrete classes have been
prototyped and tested.
The general framework offers several benefits for
the design of OS1 communication software:
The OS1 reference model suggests that each layer
or ASE should be encapsulated. The general
framework strongly upholds this principle.
The OS1 reference model suggests that layer-entities/
ASEs interact with each other by sending
messages, and our design reflects this.
The design is largely language independent, so any
object-oriented language can be used.
The design not only models point-to-point communication
between layer-entities/ASEs, but also
protocols such as MHS, the Directory and communication
between separate distriiuted systems.
The design is as general as possible, which allows
developers to add any specific features they require.
It also permits the design to be extended
easily as new protocols appear, simply by creating
new abstract classes or inheriting from existing abstract
classes.
We believe that as communication requirements
change and become more demanding, a fresh approach
to design is required if good quality communication
software is to be produced and maintained. The general
framework we have developed demonstrates that
the object-oriented approach can offer a more effective
and flexile method for the design and implementation
of OS1 communication software than traditional
methods.