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Systems Theory Overview
Systems theory was introduced by biologist L. von Bertalanffy in the 1930s as a modeling devise that accommodates the interrelationships and overlap between separate disciplines. The reality is that when scientists and philosophers first tried to explain how things worked in the universe, there were no separate disciplines. There were simply questions to be answered. But as we started understanding more and more, the sciences broke down into chemistry, physics, biology, and then biophysics, biochemistry, physical chemistry, etc. so that related components of a problem were investigated in isolation from one another. The Systems Theory introduced by von Bertalanffy reminds us of the value of integration of parts of a problem. Problems cannot be solved as well if they are considered in isolation from interrelated components. An enormous advantage systems analysts have in knowing the definitions of systems theory is that they present us with ideal guidelines for our initial familiarization with a new problem, which of course is a new system.
Systems Theory Terms:
Problem
A problem can be a question looking for an answer, a situation (such as an existing information system) that isn't working properly and needs improving, or a new opportunity or idea that is worthy of further consideration. In other words, when we speak of a "problem" in systems analysis and design, we don't necessarily mean that there is something wrong. We mean that there is a situation that needs to be understood and a solution to be determined.
System
From your text: A system is a set of related components that work together in a particular environment to perform whatever functions are required to achieve the system's objective.
Goal Seeking
A system is goal-seeking by definition. When the definition of a system says that a system's components work together to achieve a common objective it means that the system seeks to complete a goal. For example, the objective of the digestive system is ensure that food is digested, with some byproducts going into the related circulatory system to nurture the body and other byproducts being expelled. The objective of a payroll system is likely to be to produce complete, correct and timely output in the form of cheques, reports, and updated history files. It is important to be able to identify the objectives of any existing or new system to be able to understand it and evaluate its effectiveness. In an information system, the components include people, procedures, data, software, and hardware. Paper artifacts are part of this, such as manuals, forms, and reports.
Input
Every system has input.
Output
Every system has output. It is fair to say that a system may be evaluated by determining if its output results in the achievement of its objective.
Feedback
To be effective and efficient a system needs a feedback mechanism that can ascertain whether the outputs of the system are what they should be. If not. a system should have the ability to adjust its inputs or processes to improve the outputs. An ideal system is self-regulating. The feedback mechanism in an information system may be automated or may be manual.
Entropy
Entropy is a measure of the degree of disorder in a system. It is a familiar term in thermodynamics, when considering chemical systems, and is also relevant to information systems. The concept of entropy says that any system will tend towards disorder. Knowing that, we can put checks in place to monitor the correctness of the output of a system.
Internal Environment
A system operates in an environment with both internal and external components. Its internal environment it that part of its environment over which it has some control. If some aspect of the internal environment is causing some difficulty for the system, that aspect can be altered. For example, a particular information system operates in a particular office environment. If a requirement of the information system is that its users must collect data that hasn't been collected previously, this new activity can be asked of them.
External Environment
A system's external environment is that part of its environment over which it has no control, but it still affects the requirements of the system. For example, in a payroll system, the provincial and federal tax laws affect the procedures in the system. The tax laws must be reflected in the system, and if the laws change, the system must change to accommodate those changes. So an analyst must be aware of the requirements of both the internal and external environments in which an information system will work.
Subsystem
A system is usually composed of self-contained but interrelated systems that are called subsystems. It is important to be able to recognise these subsystems, because understanding this interdependence is vital to developing a complete system.
Supersystem
A system composed of two or more systems may be called a supersystem of those systems.
System Boundary
A system boundary may be thought of as the point at which data flows (perhaps as output) from one system to another (perhaps as input). The degree to which data is free to flow from one system to another is known as the permeability of the boundary. A permeable boundary allows data to flow freely, resulting in an open system. An impermeable boundary is one which strictly controls (or even restricts) the acceptance or dispensing of data, resulting in a closed system.
Interdependence
One of the most important concepts in Systems Theory is the notion of interdependence between systems (or subsystems). Systems rarely exist in isolation. For example, a payroll system has to access and update a personnel system. It is important for an analyst to identify these interdependence early. It may be the case that changes you make to one system will affect another in ways you haven't considered, or vice versa.
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