Visibility of Control in Adaptive Systems

Adaptive systems respond to changes in their internal state or external environment with guidance from an underlying control system. ULS systems are particularly likely to re- quire dynamic adaptation because of their decentralized con- trol and the large number of independent stakeholders whose actions are integral to the system's behavior. Adaptation may take various forms, but the system structure will al- most inevitably include one or more closed feedback loops. We argue that adaptability is a characteristic of a solution, not of a problem, and that the feedback loop governing con- trol of adaptability should be explicit in design and analysis and either explicit or clearly traceable in implementation.