SHOP: Simple Hierarchical Ordered Planner

TLDR

SHOP is a domain‑independent HTN planner that generates tasks in execution order, avoiding goal‑interaction problems and enabling highly expressive domain models with complex numeric reasoning. In benchmark tests, SHOP outperformed Blackbox by several orders of magnitude and TLpian by a factor of several, despite being implemented in Lisp rather than C.

Abstract

SHOP (Simple Hierarchical Ordered Planner) is a domain-independent HTN planning system with the following characteristics. • SHOP plans for tasks in the same order that they will later be executed. This avoids some goal-interaction issues that arise in other HTN planners, so that the planning algorithm is relatively simple. • Since SHOP knows the complete world-state at each step of the planning process, it can use highly expressive domain representations. For example, it can do planning problems that require complex numeric computations. • In our tests, SHOP was several orders of magnitude faster man Blackbox and several times faster than TLpian, even though SHOP is coded in Lisp and the other planners are coded in C.