Towards Flexible Teamwork
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Journal of Articial Intelligence Research Submitted published Towards Flexible Teamwork Milind Tamb e tambeisiedu Information Sciences Institute and Computer Science Department University of Southern California Admiralty Way Marina del Rey CA USA Abstract Many AI researchers are to day striving to build agent teams for complex dynamic multiagent domains with intended applications in arenas such as education training entertainment information integration and collective rob otics Unfortunately uncertain ties in these complex dynamic domains obstruct coherent teamwork In particular team memb ers often encounter diering incomplete and p ossibly inconsistent views of their en vironment Furthermore team memb ers can unexp ectedly fail in fullling resp onsibilities or discover unexp ected opp ortunities Highly exible co ordination and communication is key in addressing such uncertainties Simply tting individual agents with precomputed co ordination plans will not do for their inexibility can cause severe failures in teamwork and their domainsp ecicity hinders reusability Our central hyp othesis is that the key to such exibility and reusability is providing agents with general mo dels of teamwork Agents exploit such mo dels to autonomously rea son ab out co ordination and communication providing requisite exibility Furthermore the mo dels enable reuse across domains b oth saving implementation eort and enforc ing consistency This article presents one general implemented mo del of teamwork called STEAM The basic building blo ck of teamwork in STEAM is joint intentions Cohen Levesque b teamwork in STEAM is based on agents building up a partial hierar chy of joint intentions this hierarchy is seen to parallel Grosz Krauss partial Shared Plans Furthermore in STEAM team memb ers monitor the teams and individual memb ers p erformance reorganizing the team as necessary Finally decisiontheoretic com munication selectivity in STEAM ensures reduction in communication overheads of team work with appropriate sensitivity to the environmental conditions This article describ es STEAMs application in three dierent complex domains and presents detailed empirical results Intro duction teamwork cooperative eort by the members of a team to achieve a common goal American Heritage Dictionary Teamwork is b ecoming increasingly critical in many multiagent environments such as virtual training Tamb e et al Rao et al interactive education for instance in virtual historical settings Pimentel Teixeira internetbased information integra tion Williamson Sycara Decker Rob oCup rob otic and synthetic so ccer Kitano et al interactive entertainment HayesRoth Brownston Gen Reilly and p otential multirob otic space missions Teamwork in such complex dynamic domains is more than a simple union of simultaneous co ordinated activity An illustrative c AI Access Foundation and Morgan Kaufmann Publishers All rights reserved Tambe example provided by Cohen and Levesque b worth rep eating given that the dier ence b etween simple co ordination and teamwork is often unacknowledged in the literature fo cuses on the distinction b etween ordinary trac and driving in a convoy Ordinary trac is simultaneous and co ordinated by trac signs but it is not considered teamwork Driving in a convoy however is an example of teamwork The dierence in the two situ ations is that while teamwork do es involve co ordination in addition it at least involves a common team goal and co op eration among team memb ers This article fo cuses on the development of a general mo del of teamwork to enable a team to act coherently overcoming the uncertainties of complex dynamic environments In particular in these environments team memb ers often encounter diering incomplete and p ossibly inconsistent views of the world and mental state of other agents To act coherently team memb ers must exibly communicate to avoid misco ordination Further more such environments can often cause particular team memb ers to unexp ectedly fail in fullling resp onsibilities or to discover unexp ected opp ortunities Teams must thus b e capable of monitoring p erformance and exibly reorganizing and reallo cating resources to meet any contingencies Unfortunately implemented multiagent systems often fail to pro vide the necessary exibility in co ordination and communication for coherent teamwork in such domains Jennings In particular in these systems agents are supplied only with preplanned domainsp ecic co ordination When faced with the full brunt of un certainties of complex dynamic domains the inexibili ty of such preplanned co ordination leads to drastic failures it is simply dicult to anticipate and preplan for all p ossible con tingencies Furthermore in scaling up to increasingly complex teamwork situations these co ordination failures continually recur In addition since co ordination plans are domain sp ecic they cannot b e reused in other domains Instead co ordination has to b e redesigned for each new domain The central hyp othesis in this article is that providing agents with a general mo del of teamwork enables them to address such diculties Such a mo del enables agents to autonomously reason ab out co ordination and communication providing them the requisite exibility in teamwork Such general mo dels also allow reuse of teamwork capabilities across domains Not only do es such reuse save implementation eort but it also ensures consistency in teamwork across applications Rich Sidner Fortunately recent theories of teamwork have b egun to provide the required mo dels for exible reasoning ab out teamwork eg joint intentions Cohen Levesque b Levesque Cohen Nunes SharedPlan Grosz Grosz Kraus Grosz Sidner and joint resp onsibility Jennings are some of the prominent ones among these However most research eorts have failed to exploit such teamwork theories in building practical applications Jennings This article presents an implemented general mo del of teamwork called STEAM sim ply a Shell for TEAMwork At its core STEAM is based on the joint intentions theory Levesque et al Cohen Levesque b a but it also parallels and in some cases b orrows from the SharedPlans theory Grosz Grosz Kraus Grosz Sidner Thus while STEAM uses joint intentions as the basic building blo ck of team work as in the SharedPlan theory team memb ers build up a complex hierarchical structure of joint intentions individual intentions and b eliefs ab out others intentions In STEAM STEAM co de with do cumentationtraces is available as an online App endix Towards Flexible Teamwork communication is driven by commitments emb o died in the joint intentions theory team memb ers may communicate to attain mutual b elief while building and disbanding joint intentions Thus joint intentions provide STEAM a principled framework for reasoning ab out communication providing signicant exibility STEAM also facilitates monitoring of team p erformance by exploiting explicit representation of team goals and plans If in dividuals resp onsible for particular subtasks fail in fullling their resp onsibilitie s or if new tasks are discovered without an appropriate assignment of team memb ers to fulll them team reorganization can o ccur Such reorganization as well as recovery from failures in general is also driven by the teams joint intentions STEAMs op erationalization in complex realworld domains describ ed in the next sec tion has b een key in its development to address imp ortant teamwork issues discussed ab ove It has also led STEAM to address some practical issues not addressed in teamwork the ories One key illustration is in STEAMs detailed attention to communication overheads and risks which can b e signicant STEAM integrates decision theoretic communication selectivity agents delib erate up on communication necessities visavis incoherency in teamwork This decision theoretic framework thus enables improved exibility in commu nication in resp onse to unexp ected changes in environmental conditions Op erationalizing general mo dels of teamwork such as STEAM necessitates key mo di cations in the underlying agent architectures Agent architectures such as Soar Newell RAP Firby PRS Rao et al BB HayesRoth et al and IRMA Pollack have so far fo cused on individual agents exible b ehaviors via mech anisms such as commitments and reactive plans Such architectural mechanisms need to b e enhanced for exible teamwork In particular an explicit representation of mutual b eliefs reactive team plans and team goals is essential Additional typ es of commitments suitable for a team context may need to b e emb o died in the architectures as well Without such architectural mo orings agents are unable to exploit general mo dels of teamwork and reason ab out communication and co ordination This view concurs with Grosz who states that capabilities for teamwork cannot b e patched on but must b e designed in from the start Our op erationalization of STEAM is based on enhancements to the Soar architecture Newell plus a set of ab out domainindep ende nt Soar rules Three dierent teams have b een develop ed based on this op erationalization of STEAM These teams have a complex structure of teamsubteam hierarchies and op erate in complex environments in fact two of them op erate in a commerciallydevelop ed simulation environment for training This article presents detailed exp erimental results from these teams illustrating the b enets of STEAM in their development STEAM is among just a very few implemented general mo dels of teamwork Other mo dels