Hierarchical task network

In artificial intelligence, hierarchical task network (HTN) planning is an approach to automated planning in which the dependency among actions can be given in the form of hierarchically structured networks. Planning problems are specified in the hierarchical task network approach by providing a set of tasks, which can be: primitive (initial state) tasks, which roughly correspond to the actions of STRIPS; compound tasks (intermediate state), which can be seen as composed of a set of simpler tasks; goal tasks (goal state), which roughly corresponds to the goals of STRIPS, but are more general.

Source: Wikipedia — Hierarchical task network (CC BY-SA 4.0)