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1.2 representing IT support of businesses

1.2.1 what systems?

POSD is a notation for representing the structure of systems.

Another part of this POSD presentation explains what is meant by the term "representing the structure of systems". However it does not say which systems are the subjects of such representations. This part of the presentation addresses that question.

1.2.2 multi-level views of a system

Suppose that there is a need to develop IT support for a construction company. The designer of the IT support would need to develop system views of the company at a number of levels as shown in the diagram below.

multi-level view of a system

Note that the arrows in the fourth level of the diagram above indicate that each software system may support more than one process and be supported by more than one hardware system. Similar observations can be made about the other levels.

The reader can click on each of the five levels in the diagram to see an example of a system view at that level. The views shown are not very detailed. They could have been much more detailed. However the detailed views might have been too complex for one diagram. They could have been replaced with hierarchical structures. Each hierarchical structure would represent the system view at its level at a number of levels of detail. Click here to see an example of such an hierarchical structure.

The designer must look at a number of system views in order to bridge the gap between the business level view of a problem and an IT solution to the problem. However the same fixed set of system views (such as the set of five shown above) should not be imposed on all problems. The actual number and nature of the system views required will depend on the type and complexity of the problem.

The designer of the system would need to represent the structure of the system view at each of these levels and need to be able to represent how the lower level structures contributed to the higher level ones. POSD examples will show how this may be done.

last revision: 21st June 1997