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Functions

A function is what a system does. A function is what one of the systems in an interaction does. The list of functions that a single system supports can be quite large. Of course functions can be defined at any level of system interaction but when functions interact with actors their interface is the domain of the systems engineer. The systems engineer attempts to specify the outcome of a function and its IO without saying how it will accomplish anything. In the requirements analysis of a system this can be the most tedious part.

Algorithm

Functions are often expressed as algorithms. An algorithm is merely a sequence of steps that describe an activity that has a desired goal. The algorithm of a function is the domain of the designer.

You can see where the tension would occur. When the systems engineer tries to influence the design, he is overstepping his boundary. When the designer attempts to change the external interface, he comes face to face with the systems engineer. They both care about different aspects of the system. The systems engineer cares about the overall flow of information about the system while the designer is concerned with the efficiency of his design. Since data structures influence design there is a tension. Sometimes it works out ok.

Functions are always allocated to physical system components. Functions often have time constraints that links them to temporal states. Functions are aggregated into a feature which is the goal of the functions.

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