From “Formal Methods” to System Modeling - Formal Methods and Hybrid Real-Time Systems - page 25

• System models: describing the logical and technical behavior and

structure of the system and software under development,

• Quality models: describing quality aspects of the system and software

under development or its development process (see [3]),

• Cost models: calculating the cost and required budget for a development

project,

Development process models: describing the structure of the development
process (see [5]).
These models are used as the basis for the engineering of software intensive
systems. In particular, for the planning of a development project and in requirements
engineering such models are indispensable. The formality of these models is only one
aspect. Of course, if tool support is requested for the application of these models,
formalization is inevitable.

•

levelsofabstraction

hierarchicaldecomposition

propertyrefinement

Fig. 1. Three Dimensions of Software Development

In the following we concentrate rather on the system modeling aspect. In the
development of large complex software system it is simply impossible to provide one
comprehensive model for the system in only one step. Rather we
•

specify a system or subsystem first in terms of its interface,

• add stepwise details by refinement,

• give several views,

• decompose the hierarchically system into components,

construct a sequence of models on different levels of abstraction.
Each step in these activities introduces models, refines them, or integrates them.
Concentrating on the modeling issues we have to manage the following tasks:
•

•

selection of the appropriate model concept for an aspect,

• identifying and documenting all the properties for a model,

• integrating several views into an overall model,

• decomposing a model hierarchically into components.