Towards a Formal Framework for Hybrid Planning in Self-Adaptation

Decision-making approaches in self-adaptation face a fundamental trade-off between quality and timeliness of adaptation plans. Due to this trade-off, designers often have to make an offline compromise between finding adaptation plans quickly and finding closer-to-optimal plans that demand longer computation times. Recent work has proposed that hybrid planning can resolve this trade-off dynamically, achieving higher utility than either fast or slow approaches individually. The promise of hybrid planning is to combine multiple decision-making approaches at run time to produce adaptation plans of the high quality within given time constraints. However, the diversity of decision-making approaches makes the problem of hybrid planning complex and multi-faceted. This paper advances the theory of hybrid planning by formalizing the central concepts and four sub-problems of hybrid planning. This formalization can serve as a foundation for creating and evaluating hybrid planners in the future.