Landscape of Solution Approaches

1
Landscape of Solution Approaches

• coordinated action

Coordinating Executing Plans
Heterogeneous P/S Agents
Negotiation-based Approaches
Self- Scheduling Systems
Market Mechanisms
Constraint-based Resource Mgnt.

• independent jobs/goals

• optimized team behavior

• high dynamics

2
Coordinating executing plans

• Multiagent Plan execution semantics
• Domain-independent Teamwork Collaboration
• Example Joint Intentions

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3
Explicit/Procedural Plan Coordination (without
underlying semantics)

• Simple Idea Provide specific plans to coordinate
• When at holding point, scout flies to battle
  position then informs those waiting at holding
  point that the battle position is scouted
• To fly in formation, each agent is assigned
  someone to follow in formation (follow-the-leader)
  
• Problem Fragile! Difficult to get it right for
  all contingencies

4
Problems with Explicit, semantics-free PlansNo
framework to anticipate failures numerous ad-hoc
plans

• Upon reaching the holding area, the company
  waited, while the scout started flying forward.
• Unfortunately, the scout unexpectedly crashed
  into a hillside. Hence, the rest of the company
  just waited indefinitely at the holding area,
  waiting to receive a message from the (crashed)
  scout that the battle position was scouted.
• Upon recognizing that the mission was completed,
  one company member (the commander) returned to
  home base, abandoning others at the battle
  position
• The commanders follower was unexpectedly shot
  down, and hence it failed to coordinate with
  others in its company.

5
Joint-Intentions lead to Execution Robustness

• Team goals/plans are represented explicitly
• Individual intentions scheduled actions
• Team members have commitments and
  responsibilities toward others when executing a
  team activity.
• Commitments to not just local actions, but
  achievement of overall goal
• Other approaches possible, e.g. SharedPlans
  Grosz Kraus 96
• Tries to avoid need for joint mental attitude
• Hierarchical plans

6
Explicit Model of Teamworkusing Joint-Intentions
(Cohen Levesque)

• A team ? jointly intends a team action
• if team members are jointly committed to
  completing that team action
• while mutually believing that they were doing it
  (not unintentional)
• Joint commitment is defined as joint persistent
  goal (JPG)
• JPG (?,p) Team ? has a joint persistent goal
  to achieve p
• entire team can be treated as jointly committed
  to a team plan
• Bunch of helicopters flying on own to a waypoint
  IS NOT the same as a team flying to a waypoint.
• Difference may be only in mental state, if
  nothing goes wrong
• Success of the team may not require each
  individual to successfully complete its journey

7
Conditions for JPG to Hold

• All team members ? in ? mutually believe p
  currently.
• All team members mutually know they want p
  eventually.
• All team members mutually believe that until p is
  mutually known to be achieved, unachievable or
  irrelevant, they mutually believe that they each
  hold p as a weak achivement goal (WAG)
• Either privately believes p and wants p
  eventually,
• Or, having privately discovered p to be achieved,
  unachievable or irrelevant, ? has committed to
  having this private belief become ?s mutual
  belief

8
ExampleSTEAMa Shell for TEAMwork Tambe

• Computationally tractable Joint-Intention
  framework to handle
• Communication costs
• Uncertainty about state other team members
• Single and Multiple Team member failure
• Evolving hierarchy of joint events
• Domain-independent approach to establish and
  maintain joint-intentions
• Organizational roles dependencies
• Folds in some of the hierarchical representation
  used by SharedPlans theory

9
STEAM Overview

• Team-oriented Programs Explicit team reactive
  plans/operators
• Hierarchically expand into individual
  plans/operators
• Roles, e.g., lead role in formation flying, with
  constraints
• Domain-independent plans for
• Coherence Preservation establish joint
  commitments
• Maintenance Repair monitor and fix, or
  decommit

Execute mission
Company A
Engage
Attack Platoon A1
Company A
Fly-flight-plan
Fly-route
Individual A1-a
Employ-weapons
Follow
Lead
10
Situated Plans (Reactive Plans)

• Situated/reactive plan consists of
• Preconditions, matched with agents beliefs
• Termination conditions, to terminate plan when
  matched
• Plan body to execute when plan activated
• May invoke external or internal or no action
• Example Plan Attend-Agents-Workshop
• Precondition Saw agents workshop call for
  participation
• Body Register for workshop, fly, attend
  sessions, fly-back..
• Termination condition Attended agents workshop

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Coherence Preservation Establish Commitments

• Team leader broadcasts a message to the team ? to
  establish PWAG (persistent weak achievement goal)
  to operator OP. Leader now establishes PWAG. If
  JPG(?,OP) not established within time limit,
  repeat broadcast.
• Subordinates ?i in the team wait until they
  receive leaders message. Then, turn by turn,
  broadcast to ? establishment of PWAG for OP and
  establish PWAG.
• Wait until ? ?i, ?i establish PWAG for OP
  establish JPG(?,OP)

Hierarchy of jointly committed team plans implies
coherence when executing terminating team plans
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Maintenance Repair

• All team plans executed by forming terminating
  joint commitments
• Request-confirm exchanges so all team members
  select commit
• Establish mutual belief for achieved,
  unachievable, to terminate
• Explicit constraints on individual/subteam roles
  team goal
• Form, repair, terminate team plans All
  communication in STEAM
• Example Team of helicopters jointly commit to
  execute mission
• If commander privately believes mission
  unachievable
• Commander must establish mutual belief in
  termination condition
• It communicates (and confirms) mission
  unachievable no one left behind

13
Maintenance and Repair, cont.

• Scouting failure example Wait-for-battle-position
  -scouted is the team plan
• AND-combination Scout and Non-scout roles in
  team plan
• If scout crashes, the scout role is not fulfilled
• AND-combination implies that the team plan fails
• Joint commitment to replan by reorganization, if
  critical failures
• Determine candidates for roles via capability
  matching
• Candidates for roles ensure no conflicting
  critical commitments
• Individual/subteam may volunteer
• If multiple candidates, compare based on
  capability
• Highest capability agent wins
• Scouting failure example continued
• Locate other pilots capable of scouting
• New candidate scout ensure no conflicting
  commitments
• Candidate scout(s) volunteer
• Best capability scout wins