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

11.4 Essential Specification Modelling 347
in depth. Simultaneously, three sorts of representations are used to model a
conceptual solution:
– Architecture Structure Diagrams;
– Message Flow Diagrams;
– Object Class Diagrams.
3. Structural aspects of a conceptual solution and/or prescribed structure are denoted
in Architecture Structure Diagrams which are free style graphical representations.
Architecture design decisions must be documented in the Requirements Catalogue.
Response time requirements on the system level are denoted textually for the
modules in the Architecture Structure Diagrams.
4. Message Flow Diagrams are used to model a conceptual solution as collaborating
processes that exchange messages. Various types of flows are used to show asynchronous
communication, continuous communication, etcetera. Complex systems
are modelled by using scenarios.
5. Information from the Initial Requirements Description that is not modelled otherwise
is transferred to Listed Requirements in the Requirements Catalogue.
6. Message Flow Diagrams show flows where data objects are exchanged between
process objects. Data objects can represent complex data structures. Relations
between objects that form and use these structures are modelled in Object Class
Diagrams. Figure 11.9 shows that the modelling of Object Class Diagrams can
be performed simultaneously with the modelling of the Message Flow Diagrams.
Generalisation-specialisation relations, whole-part relations and other relations
show the conceptual structure of a problem domain;
7. Instance Structure Diagrams are used for the design of a system’s channel structure.
They are also used as preparation of a Unified Model. These diagrams model the
physical and logical structure of a problem domain in the form of a structure of
channels between process objects, terminators and clusters.
8. A formal Unified Model in POOSL describes the:
– structure of the systems that is visualised in Instance Structure Diagrams;
– behaviour of all cluster classes, process classes and data classes.
9. There is a strong interaction between the various modelling activities and the creation
of the Unified Model. New objects or new flows may be found, or previously
defined objects or flows may have to be modified. This leads to changes in Object
Class Diagrams and Message Flow Diagrams. Changes in structure can be
performed in Instance Structure Diagrams using Behaviour-Preserving Transformations.
10. The Requirements Catalogue is updated and extended continuously during the
whole modelling process.