Execution Semantics of Behavior Trees in Robotic Applications

2024-07-31

AI Summary

Behavior trees (BTs) are widely adopted in robotics, yet their lack of a unified, formal execution semantics leads to behavioral inconsistencies across implementations, impeding cross-platform deployment and reliability verification. To address this, we propose the first complete and unambiguous formal semantics for BTs in robotic applications. Our approach models BTs using abstract data types (ADTs), rigorously defining node semantics, control-flow mechanisms, and state-transition rules. The semantics is structured to comprehensively cover all standard node types—including composites, decorators, and leaf nodes—as well as their composition logic. This framework fills a critical theoretical gap in BT formalization, enabling semantic consistency checking, interoperability among BT toolchains, and development of high-assurance control software. By establishing a mathematically grounded foundation, our work advances BT standardization and supports the construction of trustworthy robotic systems.

Technology Category

• Intelligent Robots: Behavior Learning & Control
• Humans and AI: Human-Aware Planning and Behavior Prediction
• Planning, Routing, and Scheduling: Model-Based Reasoning

Application Category

• Semantics and Knowledge: Data modeling to support human-machine intelligence, including LLMs agents, intelligent system behavior, explanations, and user-friendly interactions
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications

Abstract

Behavior Trees (BTs) have found a widespread adoption in robotics due to appealing features, their ease of use as a conceptual model of control policies and the availability of software tooling for BT-based design of control software. However, BTs don't have formal execution semantics and, furthermore, subtle differences among implementations can make the same model behave differently depending on the underlying software. This paper aims at defining the execution semantics of behavior trees (BTs) as used in robotics applications. To this purpose, we present an abstract data type that formalizes the structure and execution of BTs. While our formalization is inspired by existing contributions in the scientific literature and state-of-the art implementations, we strive to provide an unambiguous treatment of most features that find incomplete or inconsistent treatment across other works.

Problem

• Defining formal execution semantics for Behavior Trees in robotics
• Addressing inconsistent BT implementations causing varying behaviors
• Providing unambiguous treatment of BT features across implementations

Innovation

• Defines formal execution semantics for Behavior Trees
• Introduces abstract data type for BT structure
• Provides unambiguous treatment of BT features