Page 158 - DCAP405_SOFTWARE_ENGINEERING

Unit 9: System Engineering

9.4 Role of Modeling and Simulation Notes

Definitions of Systems and Models

A system is an assemblage of interrelated parts that work together by way of some driving
process (see Figure 9.9). Systems are often visualized or modeled as component blocks that have
connections drawn between them. For example, the illustration below describes the interception
of solar radiation by the Earth. In this system, the Earth and Sun, the parts or component blocks,
are represented by two colored circles of different size. The process of solar emission and the
interception of the Sun’s emitted radiation by the Earth (the connection) is illustrated by the
drawn lines.
Figure 9.9: Simple Visual Model of Solar Radiation being Emitted from
the Sun and Intercepted by the Earth

Characteristics of a System

Most systems share the same common characteristics. These common characteristics include the
following:

1. Systems have a structure that is defined by its parts and processes.
2. Systems are generalizations of reality.
3. Systems tend to function in the same way. This involves the inputs and outputs of material
(energy and/or matter) that is then processed causing it to change in some way.
4. The various parts of a system have functional as well as structural relationships between
each other.

5. The fact that functional relationships exist between the parts suggests the flow and transfer
of some type of energy and/or matter.
6. Systems often exchange energy and/or matter beyond their defined boundary with the
outside environment, and other systems, through various input and output processes.
7. Functional relationships can only occur because of the presence of a driving force.
8. The parts that make up a system show some degree of integration - in other words the
parts work well together.

Properties of a System

Within the boundary of a system we can find three kinds of properties:
1. Elements are the kinds of parts (things or substances) that make up a system. These parts
may be atoms or molecules, or larger bodies of matter like sand grains, rain drops, plants,
animals, etc.

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