The central issues to be resolved by the new theories are the determination of
the control system structure. Which variables should be measured, which inputs
should be manipulated and which links should be made between the two sets?
... The gap is present indeed, but contrary to the views of many, it is the
theoretician who must close it.
A similar observation that applications seem to be ahead of formal theory was made by Findeisen et al. (1980) in their book on hierarchical systems (p. 10). Many authors point out that the need for a plantwide perspective on control is mainly due to changes in the way plants are designed – with more heat integration and recycle and less inventory. Indeed, these factors lead to more interactions and therefore the need for a perspective beyond individual units. However, we would like to point out that even without any integration there is still a need for a plantwide perspective as a chemical plant consists of a string of units connected in series, and one unit will act as a disturbance to the next, for example, all units must have the same throughput at steady-state.