Eran Gat proposed one of the best known and most popular approaches to hybrid control: the Three Tier Architecture (3T) (Kortenkamp, 1998). As most hybrid control paradigms, 3T has a behavior layer, a sequencer and a deliberative layer. In 3T, algorithms are split into three categories: no memory, state-reflecting memory or state-based prediction alforithms, from more reactive to more deliberative components. Their function is the following:

-Memoriless algorithms inhabit the control components (skills)
-Memory-based algorithms inhabit the sequencer
-Predictive algorithms inhabit the deliberator

The main differences between 3T implementations lies in who really rules the system: reactive or deliberative layer (sequencer is always arbitrating :P). Dad, mom and kid in any combination! :D:D