The Functional Parameter Space

Stakeholder requirements will not only define capabilities, such as being able to transmit information , in terms of the parameters associated with the capabilities, such as bit rate, error rate, latency, etc. but will deflne restrictions on the values these parameters are allowed to have, and the same is true of the parameters associated with the various aspects of performance, such as reliability, maintainability, and safety. These restrictions result in restrictions on the values of the functional parameters of the corresponding functional element If we visualise the space spanned by all the functional parameters, the functional parameter space, then these restrictions define a volume within that space, and the solution is constrained to lie within that volume. The size and dimensionality of that volume depends on the nature of the restrictions, as the simple case of two parameters, x and y, in Fig. C4.9 demonstrates. 

However, in addition to restrictions of the type illustrated in Fig. C4.9, we have the universal requirement of maximising the return on investment, U. That quantity is a function of the functional parameters, and at some point in state space it will take on its maximal value. In Chapter C6 we shall show that, as a result of the definition of U, the maximum lies within the allowed volume. 

When the functional model is realised as an operating plant, the parameters will all take on values somewhere within the allowable volume. That is, at any one point in time, the state of the plant will be a point in the allowable volume and, due to both internal (e.g. random failures) and external (e.g. temperature, interest rate, etc.) factors, this point will change during the operational lifetime, describing a trajectory in state space. In general this trajectory cannot be predicted, but it is 

Aslaksen, E.W. Designing Complex Systems - Foundations of design in the functional domain. CRC Press (2008) 

English Verb Classes and Alternation A Preliminary Investigation. The University of Chicago Press (1993) 

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