1.6 Types of systems The frame of reference within which one views a system is related to the use of the systems approach for analysis. Systems have beenclassified in different ways. Common classifications are: (1) physical or abstract, (2) open or closed, and (3) “man – made” information systems.
1.6.1 Physical or abstract systems Physical systems are tangible entities thatmay be static or dynamic in operation. For example, the physical parts of the computercenter are the officers, desks, and chairs that facilitate operation of the computer. They can be seen and counted; theyare static. In contrast, a programmed computer is a dynamic system. Data, programs, output, and applications change as the user’s demands orthe priority of the information requested changes. Abstract systems are conceptual or non-physical entities. They may be as straightforward as formulas of relationshipsamong sets of variables or models – the abstract conceptualization of physical situations
. A model is a representation of a real or a planned system. The use of models makes it easier for the analyst to visualize relationships in the system under study. The objective is to point out the significant and the key interrelationships of a complex system.
1.6.2 Open or Closed Systems
Another classification of systems is based on their degree of independence. An open system has many interfaces with its environment. It permits interaction across its boundary; it receives inputs from and delivers outputs to the outside. An information system falls into this category, since it must adapt to the changing demands of the user. In contrast, a closed system is isolated from environmental influences. In reality, a completely closed system is rare. In systems analysis, organizations, applications and computers are invariably open, dynamic systems influenced by their environment.
Five important characteristics of open systems can be identified. 1. Input from outside:
Open systems are self – adjusting and self-regulating. When functioning properly, an open system reaches a steady state or equilibrium. In a retail firm, for example, a steady state exists when goods are purchased and sold without being either out of stock or overstocked. An increase in the cost of goods forces a comparable increase in prices or decrease in operating costs. This response gives the firm its steady state. 2. Entropy:
All dynamic systems tend to run down over time, resulting in entropy or loss of energy. Open systems resist entropy by seeking new inputs or modifying the processes to return to a steady state. In our example, no reaction to increase in cost of merchandise makes the business unprofitable which could force it into insolvency – a state of disorganization. 3. Process, output and cycles:
Open systems produce useful output and operate in cycles, following a continuous flow path. 4. Differentiation:
Open systems have a tendency toward an increasing specialization of functions and a greater differentiation of their components. In business, the roles of people and machines tend toward greater specialization and greater interaction. This characteristic offers a compelling reason for the increasing value of the concept of systems in the systems analyst’s thinking. 5. Equifinality:
The term implies that goals are achieved through differing courses of action and a variety of paths. In most systems, there is more of a consensus on goals than on paths to reach the goals. Understanding system characteristics helps analysts to identify their role and relate their activities to the attainment of the firm’s objectives as they undertake a system project. Analysts are themselves part of
the organization. They have opportunities to
adapt the organization to changes through computerized application so that the system does not “run down.” A key to this process is
information feedback from the prime user
of the new system as well as from top management.
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