Collaborative Plans for Complex Group Action The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Grosz, Barbara J. and Sarit Kraus. 1996. Collaborative Plans for Complex Group Action. Artificial Intelligence 86(2): 269-357. Published Version http://dx.doi.org/10.1016/0004-3702(95)00103-4 Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:2562070 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Collab orative Plans for Complex Group Action Barbara J Grosz Division of Applied Sciences Harvard University Cambridge MA USA groszeecsharvardedu Sarit Kraus Department of Mathematics and Computer Science Bar Ilan University Ramat Gan Israel saritcsbiuacil and Institute for Advanced Computer Studies University of Maryland College Park MD Note This article app ears in Articial Intel ligence This pap er is an extension of our pap er in IJCAI Grosz and Kraus We thank Joyce Friedman for many thoughtprovoking questions and Karen Lo chbaum for the same and for helpful comments on many drafts We also thank Michael Bratman David Israel and Martha Pollack for comments on earlier versions and the anonymous reviewers for their helpful suggestions and illuminati ng comments This researchwas initiated when the rst author was a Harold Perlman Visiting Professor Hebrew University Jerusalem Partial supp ort for the rst author was provided by U S WEST Advanced Technologies The second author was supp orted in part by NSF GrantNumber IRI and the Israeli Science Ministry grant No Abstract The original formulation of SharedPlans Grosz and Sidner a was develop ed to provide a mo del of collab orative planning in whichitwas not necessary for one agenttohaveintentionsto toward an act of a dierent agent Unlike other contemp oraneous approaches Searle this formulation provided for two agents to co ordinate their activities without intro ducing any notion of irreducible jointintentions However it only treated activities that directly decomp osed into singleagent actions did not address the need for agents to commit to their joint activity and did not adequately deal with agents having only partial knowledge of the way in whichtoperform an action This pap er provides a revised and expanded version of SharedPlans that addresses these shortcomings It also reformulates Pollacks denition of individual plans Pollack to handle cases in which a single agent has only partial knowledge this reformulation meshes with the denition of SharedPlans The new denitions also allow for contracting out certain actions The formalization that results has the features required by Bratmans account of shared co op erative activity Bratman and is more general than alternative accounts Levesque Cohen and Nunes Sonenb erg et al i Contents Intro duction Examples of Collab orative Plans Overview of the Mo del Supp orting Denitions and Notation Recip e Notation Subsidiary Predicates and Functions Basic Mo dal Op erators Attitudes of Intention Typ es of Intending Mo dal Op erators for Attitudes of Intention Axioms for Intention Op erators MetaPredicates for the AbilitytoAct Complex Actions for Planning Individual Plans Full Individual Plans Partial Individual Plans Capabilities to Perform Actions in Individual Plans SharedPlans and Intendingthat Denition of SharedPlan Full SharedPlans Intentionsthat in SharedPlans P artial SharedPlans Capabilities to Perform Actions in SharedPlans An Example SharedPlan for Dinner Implications of the Formalization Comparison with Alternative Approaches Conclusions and Future Work A Abilities and Beliefs A Pro of of Theorem T BFormal Plan Denitions and Additional Intentionthat Axiom ii List of Figures Key comp onents of collab orative plans Recip e tree and the other leaf no des are basiclevel actions The denition of IntTo Axiom schema to avoid conicting intentions Intentions and b eliefs Denition of CBA can bring ab out and CC can contract Denition of CBAG can bring ab out group and CCG can contract group Denition of GTD get to do English description of the FIP full individual plan denition FIP Core case FIP Contractingout case English description of the PIP partial individual plan denition PIP Finding a recip e PIP Core case PIP Contractingout case PIP Unreconciled case Denition of SP SharedPlan English description of the FSP full SharedPlan denition FSP Core case singleagent action FSP Core case multiagent action Contracting in a FSP singleagent subactions Contracting in a FSP multiagent subactions Axioms for intendingthat Helpfulb ehavior axiom for intendingthat English description of the PSP partial SharedPlan denition PSP Finding a recip e PSP Core Case singleagentact PSP Core Case multiagentact PSP Unreconciled case Beliefs and capabilities to p erform actions in FIP and the denition of BCBA b elieve can bring ab out and related theorem Beliefs and capabilities to p erform actions in PIP and the denition of WBCBA weakly b elieve can bring ab out Beliefs and capabilities to p erform actions in FSP and the denition of MBCBAG mutuallyb elievedcanbri ngab outgroup Beliefs and capabilities to p erform actions in PSP and the denition of WMBCBAG weakly mutually b elieve can bring ab out group Denition of Full Individual Plan Denition of Partial Individual Plan Denition of Full SharedPlan FSPC Contracting in FSP The p erformance of the contracting action in the contracting cases of FSP MP Memb er of the group p erforms the contracting action SGPsubgroup p erforms the contracting action Denition of Partial SharedPlan iii PSP Contractingout case singleagent PSP Contractingout case multiagent Another helpfulb ehavior axiom for intendingthat iv Intro duction Co op erative problem solving by teams comp osed of p eople and computers requires collab oration and communication Collab oration is a sp ecial typ e of co ordinated activity one in which the par ticipants work jointly with each other together p erforming a task or carrying out the activities needed to satisfy a shared goal Because collab orative action comprises actions by dierent agents collab orative planning and activityinvolvetheintentions of multiple agents As a result collab orative plans cannot b e recast simply in terms of the plans of individual agents but require an integrated treatment of the b eliefs and intentions of the dierentagents involved Furthermore the collab orative planning pro cess is a renement pro cess a partial plan description is mo died over the course of planning by the multiple agents involved in the collab oration Thus capabilities for collab oration cannot b e patched on but must b e designed in from the start Searle Grosz and Sidner a In this pap er wepresent a formal mo del of collab orative plans that deals more completely with collab oration than previous existing theories of actions plans and the plan recognition pro cess This mo del grew out of an attempt to provide an adequate treatment of the collab orative b ehavior exhibited in dialogues Grosz and Sidner The collab orative prop erty of dialogue aects communication in all mo dalities and thus is a factor that must b e reckoned with in developing more advanced systems for humancomputer communication regardless of the mo dality of commu nication Communication and collab oration also playseveral imp ortant roles in multiagent action First communication provides a means for working together to achieve shared ob jectiv es Bond and Gasser Davis and Smith Durfee Conry et al Werner inter alia most multiagent systems in which the agents need to co ordinate their activities incorp orate some mechanism for agents to communicate Second manymultiagent situations require that agents have an ability to plan and act collab oratively the avoidance of conicting actions is a necessary part of such capabilities but is not sucient in itself Kraus and Wilkenfeld Zlotkin and Rosenschein Gasser Kraus and Lehmann inter alia For example in some cases agents must decide collectively on the approach they will take to acting ie the constituent actions they will p erform and negotiate ab out resp onsibilities for p erforming the subsidiary ac tions entailed The mo del presented here is intended to provide the basis for constructing computer agents that are fully collab orativeaswell as to provide a framework for mo delling the intentional comp onent of dialogue Grosz and Sidner Lo chbaum The original formulation of the SharedPlan mo del of collab orative planning Grosz and Sidner a extended Pollacks mental state mo del of plans Pollack c Pollack to the situa tion in whichtwo agents together form a plan to p erform