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

346 SHE Framework
Object
Class
Diagrams
Initial Requirements Description
Message Flow Diagrams
Unified Model
(POOSL)
Requirements Catalogue
Instance
Structure
Diagrams
Arch/
Impl.
Structure
Diagrams
Figure 11.9: Development of Models in the Course of Time
2. Extended Specification which consists of
a. Extended System model
b. Extended Environment model
In the above list we emphasise again that in general the environment of the system must
be modelled separately. The flow of activities in one phase of the modelling process can
be as follows.
1. In the first stage of the essential modelling process the Initial Requirements must be
completed as much as possible. In general, industrial contracting parties will not
produce a ’complete’ Initial Requirements Description. Our method requires as
input an explicit purpose description and a separate description of prescribed technologies
and topologies. Further interviews must guarantee that the requirements
list is as complete as possible. Preferably, superfluous implementation details are
separated from essential functional requirements.
2. Based on an Initial Requirements Description one or more conceptual solutions
must be found. A conceptual solution in this context is a feasible idea that matches
the system’s purpose description and that gives initial structure to the model.
Possible alternative conceptual solutions must be evaluated. The exploration of a
solution requires the creation of a preliminary model. The system level structure
(architecture) and the main processes and their tasks must be explored. Figure
11.9 shows the complete development process for one chosen conceptual solution
time of the development proces