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

11.4 Essential Specification Modelling 365
Message Flow Diagrams. The exchange of messages is visualised in Message Flow
Diagrams, however the order in which messages are processed is mainly described
in scenario narratives. The information of all scenarios for each class must be
combined to be able to write a complete behaviour description.
Besides the structure description that can be derived straightforward from the diagrams,
the internal dynamic behaviour of classes must be created. Data objects have a simple
direct relation between messages and methods. However process objects must be designed
carefully as a collection of methods, each of which is rather independent of the
process object’s messages interface.
In general, processes are described taking the following into account:
methods can be used to create named states according to the problem domain;
messages can be received conditionally, so that a process can autonomously decide
which messages it wants to receive when;
the order of messages in a scenario can be described straightforwardly;
messages can be used to model events and responses;
tail recursion can be used for the description of non terminating behaviour;
interrupts can be used for the reception of messages during the execution of some
behaviour;
aborts can be used to describe behaviour that can be stopped without the need for
resumption;
alternative behaviours can be described as non-deterministic choices;
asynchronous communication can be realised by defining an additional buffer
object;
the use of channel names as destinations can conflict with Behaviour-Preserving
Transformations;
sequential behaviour does require waiting for a reply after each sending action.
The purpose of the Essential Unified Model is an extensive exploration of the wishes
of the users, customers, employers, and various experts. The model must become
a correctly executing specification. Currently tools are under development to enable
simulation.
A concrete example of a POOSL description is given in Chapter 12. An extensive
description of the use of the language is beyond the scope of this thesis. Teaching
material must be developed as future research based on concrete examples.