Goals in the context of BDI plan failure and planning

Abstract

We develop a Belief-Desire-Intention (BDI) style agent-oriented programming language with special emphasis on the semantics of goals in the presence of the typical BDI failure handling present in many BDI systems and a novel account of hierarchical lookahead planning. The work builds incrementally on two existing languages and accommodates three type of goals: classical BDI-style event goals, declarative goals, and planning goals. We mainly focus on the dynamics of these type of goals and, in particular, on a kind of commitment scheme that brings the new language closer to the solid existing work in agent theory. To that end, we develop a semantics that recognises the usual hierarchical structure of active goals as well as their declarative aspects. In contrast with previous languages, the new language prevents an agent from blindly persisting with a (blocked) subsidiary goal when an alternative strategy for achieving a higher-level motivating goal exists. In addition, the new semantics ensures watchfulness by the agent to ensure that goals that succeed or are deemed impossible are immediately dropped, thus conforming to the requirements of basic rational commitment strategy. Finally, a mechanism for the proactive adoption of new goals, other than the mere reaction to events, and a formal account of interaction with the external environment are provided. We believe that the new language is an important step towards turning practical BDI programming languages more compatible with the established results in the area of agent theory.

IndiGolog: A High-Level Programming Language for Embedded Reasoning Agents

“…[89,90] have proposed the CANPlan and CanPlan2 languages, that incorporate an HTN planning mechanism [33] into a classical BDI agent programming language. Earlier less formal work on this topic is reviewed in [89].…”

Golog Speaks the BDI Language

“…For instance, the full CAN [29,27] language as well as 2APL [7] and Jason [3] support so-called declarative goals, goals which go beyond "events" by decoupling goal success/failure from plan success/failure. However, the way such advanced features have been added to different BDI languages is not always uniform.…”

“…Our discussion is based on the CAN family of BDI languages [29,27] (Conceptual Agent Notation), which are AgentSpeak-like languages with a semantics capturing the common essence of typical BDI systems.…”

“…The failure of a plan should not be equated to the failure of its parent goal, as there could be alternative ways to achieve the latter. For example, suppose an agent has the goal to quench her thirst, and in the service of this goal, she adopts the subgoal of buying a can of soda [27]. However, upon arrival at the store, she realizes that all the cans of soda are sold out.…”

“…When the current strategy P 1 being pursued is not able to make a step, the agent may check the set of alternatives ∆ in the hope of finding another option P 2 for addressing e. If one is found, the agent may opt to abandon its strategy P 1 and continue with P 2 . (Details can be found in [29,27]. )…”