8.14. The usefulness of the systems concept as a decision tool is en­hanced if the system and its behavior can be described in a clear manner. Graphical representation is a classical approach. However, with a wide variety of computers now available, some type of representation that per­mits mathematical manipulation is preferred. This could take various forms, which could involve graphics, analytical descriptions, or combinations of each. For example, in risk management, graphical representation is useful but manipulation follows the rules of Boolian algebra (§12.218).

8.15. System behavior is normally described by quantitative relation­ships. For example, coolant circulating pumps may be described in terms of performance specifications such as flow rate, pressure differential, etc. On the other hand, some systems may involve qualitative or subjective inputs in addition to quantitative relationships. For example, in developing a model for a radioactive waste storage facility, technical requirements such as the desired amount and activity of radioactive isotopes are essential. However, there is also the likely need to input items such as local accept­ance considerations and regulatory requirements. Economic factors may also require input into the model.

8.16. In analytically modeling a system in such a way that associations between systems can be manipulated by computer, quantitative relation­ships can be handled in a straightforward manner. However, to permit similar computer manipulation of subjective modeling inputs, they must be quantified in some way, often a significant challenge.