Goals in the context of BDI plan failure and planning

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.