What does "robustness management" mean?

The mandatory assessment of robustness is frequently mentioned. But what does "robustness management" precisely mean?

One of the dangers in the usage of mathematical models and procedures for system optimization lie in the fact, that robustness may lack significantly, when optimization is stretched beyond the limits. Optimality and functionality are the counterparts of robustness. Therefore these have to be balanced well and explicitly being managed, especially in the case of complex systems (see What can go wrong with optimization?).

But what does "robustness" mean at all?

Robustness is a general concept for the description of system properties, which is slightly varied in different fields of application. There is no precise mathematical definition available for robustness, like is is for "stability".

Therefore we have derived a formulation from numerous existend definitions, which should be used in the following:

"Robustness is the safety against unexpected system behaviour"

Accordingly robustness is context sensitive and has to be formulated for each system individually then.

Robustness cannot be proved and evaluated dircetly. In case one can only show that a system is not robust. Mathematically the absent robustness amongst others can be expressed by following criteria:

• Instability respectively chaotic behaviour (small system inputs will result in big changes in the system outputs)
• Singularities and outliers (special single combinations of the system inputs will result in completely different system outputs)
• Bifurcations respectively multimodal system behaviour (small or unknown/random changes result in completely different modes of system behaviour)

Such criteria can be summarized to a system-specific catalog of criteria respectively collected in an expert system. These can then be used for the assessment, assuring that a system behaves according to its expectations.

We understand robustness managment as the systematic development, formal collection, maintenance and application of such criteria cataloges and expert systems for system assessment accompanying to the product development process.