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Collaborative Plans for Complex Group Action

Reference: Grosz, B. J. & Kraus, S. (1996). Collaborative Plans for Complex Group Action. Artificial Intelligence, 86(2), pp. 269–357. (Earlier: Grosz & Sidner 1990, Plans for Discourse, in Cohen, Morgan & Pollack eds. Intentions in Communication, MIT Press.) DOI · Open access PDF (Harvard DASH)

Summary

Grosz and Kraus (extending Grosz & Sidner 1990) develop SharedPlans, the canonical computational model of collaborative joint action in MAS. The 90-page AIJ paper supplies a formal account of how a group of agents can collaboratively form, maintain, and execute a shared plan for a complex action — a plan that is not simply a union of individual plans nor a single agent’s plan with delegated parts, but a genuinely group-level structure carrying mutual beliefs about who is doing what, why, and how. The framework distinguishes full SharedPlans (the group has a complete plan for the action and its sub-actions) from partial SharedPlans (the plan is incomplete and the agents are still working out subgoals). Each level of the plan carries explicit intentionsInt.To (intention to act) for individual actions, Int.Th (intention that) for actions performed by others or by the group as a whole — and mutual beliefs about the agents’ beliefs and intentions. The agents have meta-intentions to fill in the partial plan, leading to an iterative refinement process in which subgoals are negotiated, recipes are selected, and contributions are committed. The paper shows that SharedPlans support helpful behaviour — an agent who notices that another’s contribution is at risk has the meta-intention to assist — and robust dialogue — collaborative discourse is the agents’ communication about and incremental construction of the shared plan. SharedPlans is the most-cited computational framework for joint action in MAS; it inherits Bratman’s (1992) SCA philosophical commitments, makes them computationally tractable via the partial-plan refinement structure, and supplies the planning substrate for collaborative dialogue systems and (more recently) cooperative LLM-agent frameworks.

Key Ideas

  • SharedPlan as a group-level structure: a SharedPlan for an action α carries mutual beliefs about who is doing each sub-action, what recipe is being followed, and what intentions each agent holds toward each sub-action. Not reducible to a union of individual plans.
  • Full vs partial SharedPlans: a full SharedPlan has complete agreement on all sub-actions, recipes, and assignments; a partial SharedPlan is incomplete in any of these respects. Most real collaboration happens with partial plans that are incrementally refined.
  • Two intention modalities: Int.To(G, α) — agent G intends to perform α; Int.Th(G, α) — agent G intends that α (be performed by others, by the group, or come about). Joint action requires Int.Th of the joint act distributed across all participants.
  • Meta-intentions for plan completion: each agent has meta-intentions to (i) fill in incomplete sub-plans, (ii) help other agents perform their parts, (iii) communicate about the plan’s progress. These meta-intentions drive collaborative dialogue.
  • Recipes as parameterised plans: a recipe is a procedure for performing an action — a sequence of sub-actions plus the constraints among them. Multiple recipes may exist for the same action; agents must agree on which to follow.
  • Helpful behaviour as a corollary: an agent who notices another’s commitment is at risk has the meta-intention to help — not as an additional axiom but as a consequence of the SharedPlan’s structure.
  • Discourse as plan construction: collaborative dialogue is the activity of jointly constructing and refining a SharedPlan. Each utterance in collaborative discourse contributes to filling in the plan or signalling the speaker’s intentions about it. This connects SharedPlans to Grosz & Sidner’s earlier work on discourse structure.

Connections

Conceptual Contribution

  • Claim: Joint action by a group of agents requires a SharedPlan — a group-level structure carrying mutual beliefs about who is doing what, why, and how — that is genuinely collective rather than a union of individual plans. Most real collaboration involves partial SharedPlans, refined incrementally through agents’ meta-intentions to complete the plan, help one another, and communicate. Collaborative discourse is the activity of jointly constructing the SharedPlan.
  • Mechanism: Formal semantics distinguishing full and partial SharedPlans; two intention modalities (Int.To for own actions, Int.Th for actions of others / of the group); meta-intentions for plan completion, mutual support, and communication; recipes as parameterised plans; iterative refinement under partial knowledge.
  • Concepts introduced/used: SharedPlans, Mutual Belief, Collaborative Plan, Recipe (SharedPlans), Int.To / Int.Th modalities, Meta-intention, Helpful Behaviour.
  • Stance: foundational technical paper / computational framework.
  • Relates to: Computational realisation of Bratman’s (1992) Shared Cooperative Activity: SharedPlans operationalise the meshing-subplans / mutual-responsiveness / mutual-support conditions in a planning framework suitable for AI implementation. Cohen & Levesque’s Teamwork / joint-intention (1991) work is the parallel modal-logic framework — SharedPlans is the planning-theoretic counterpart, and the two are complementary rather than competing. Tuomela’s We-intentions take the opposing reductive-vs-irreducible position. Direct ancestor of the COLLAGEN collaborative-dialogue framework (Rich & Sidner 1998) and many subsequent collaborative-dialogue systems. In the LLM-agent era, SharedPlans is the obvious target architecture for cooperative multi-agent setups: meta-intentions to fill in partial plans correspond directly to LLM agents’ planning calls, helpful behaviour corresponds to mutual error-recovery, and the partial-SharedPlan refinement loop corresponds to the iterative plan-execute-revise cycle of agentic LLM workflows. The diagnosis from MAST is recognisable in SharedPlans terms: most failure modes are failures to maintain or refine the shared plan structure, not failures of individual agent capability.

Tags

#joint-action #sharedplans #grosz #kraus #collaborative-planning #foundations #multi-agent #dialogue

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