An Expressiveness Hierarchy of Behavior Trees and Related Architectures

In this letter, we provide a formal framework for comparing the expressive power of Behavior Trees (BTs) to other action selection architectures. Taking inspiration from analogous comparisons structural programming methodologies, formalise concept `expressiveness'. This leads us an expressiveness hierarchy control architectures, which includes BTs, Decision (DTs), Teleo-reactive Programs (TRs) and Finite State Machines (FSMs). By distinguishing between BTs with auxiliary variables those without, demonstrate existence trade-off in BT design readability expressiveness. We discuss what means practice.