Formulating consists of determining the system inputs, outputs, requirements, objectives, constraints. Structuring the system provides one or more me… - Harold Chestnut

In a society which is producing more people, more materials, more things, and more information than ever before, systems engineering is indispensable in meeting the challenge of complexity.

Models are used essentially for evaluation and prediction purposes as well as for the analysis and study of the different parts of the system so that the systems engineer or designer may arrive at sound engineering decisions regarding the system design.

System costs can be considered in many different ways. For example, the cost for making the system and the cost for operating it may be used as a basic for judging the total cost. The total cost may also be arrived at in another fashion, as, for example, the sum of the fixed cost, variable cost, past investment and other charges. Furthermore, in many cases where systems engineering is required several time phases are involved for which the cost factors may be significant, such as the study phase, the breadboard phase, the prototype phase, and the production phase.