1. L ９ : Collaborations Why? Terminology Coherence Coordination Reference ｓ : http://www.csd.abdn.ac.uk/~mkolling/publications/DesignMultiAgentCoordControlStigmergy.pdf

2. Why is coordination needed? Dependencies between agents actions Handle global constraints –E.g. Time, Money, or computational resources No individual have sufficient competence or resources to solve the entire problem alone

3. Coordination is needed when.. Building a house –Dependencies between agents actions (e.g. electricians and carpenters) Host a big sports arrangement, e.g. Olympics –No individuals have sufficient competence or resources to solve the entire problem alone Allocating lecture rooms to courses at a university –Handle global constraints (limited number of rooms)

4. Terminology of Coordination - I Coordination –An agents reasoning about its own and the anticipated behavior of other agents in order to ensure that the community acts in a coherent manner Coherence –Agents actions can be performed and that they do not conflict with one another

5. Terminology of Coordination - II Convention –A means of monitoring commitments in changing circumstances Commitment –An agents pledges to undertake a specified course of action

6. How to reach coherent behavior? Complete knowledge –All agents know everything about each other at all times Centralized Control –One or a few agents gather and distribute information about other agents Distributed Control –Agents know about themselves and some or only expectations about other agents

7. Fundamental Coordination Processes Mutual Adjustment Direct Supervision Standardization

8. Degrees of control in Coordination - I 1.Explicit Central Control –Procedure calls; master/slave (centralized, little adaption) 2.Explicit Synchronization and Communication –Semaphores, Monitors (operating system level), semi- centralized (resource-competing agents/threads) 3.Shared-Data Abstraction –Common Language Constructions, concurrent prolog

9. Degrees of control in Coordination - II 4.Functionally Accurate Cooperative Approach –Asynchronous Control, Adaptive to changes in semantics and temporal uncertainty (unprecise information) 5.Reasoned Control –Agents use their own and other agents’ knowledge to build/revise coordination frameworks (decentralized) 6.Evolving Interactions –Agents evolve during interaction (~ evolutionary computation, e.g. Genetic Algorithms), no shared semantics, fully adaptive

10. Behavioristic Coordination Approach 1.Internal (micro-level, inside agent) 2.External (macro-level, behavioristic, multi-agent system)... But when selecting behavioristic perspective –Agents’ actions may be incoherent even if trying to coordinate Example: 2 robots in appearantly different directions –Agents’ actions may be coherent even if uncoordinated Example: people running to shelter when raining  Need to consider internal aspects of agents (belief, desires,..)

11. Coordination as a distributed Goal- Search Problem

12. Dependencies – Weak and Strong

13. Dependencies – Uni/Bi-directional

14. Joint Goals Joint Goals basis of Joint Actions Joint actions –Sophisticated form of cooperation in which a team of agents decide to pursue a common goal in a cooperative manner Properties of joint actions: 1.Mutual responsibility –e.g. Legal 2.Joint Commitment –Pulling in the same direction 3.Mutual Supportive –Backing up each other

15. Joint Commitments Commitment with distributed state –Several agents participate Main Problems with joint commitment –Hard to be aware of each others states at all times  Divergating beliefs

16. Conventions Commitments may change over time –Due to changed environment Need conventions to describe when to change commitments 1.When to keep commitment (retain) 2.When to revise commitment (rectify) 3.When to remove commitment (abandon)

17. Example Convention Reasons for Re-Assessing Commitment: –Commitment Satisfied –Commitment Unattainable –Motivation for commitment no longer present Actions: –R1: If Commitment Satisfied OR Commitment Unattainable OR Motivation for Commitment no longer present Drop Commitment

18. Joint Action Example Invoke when: –Status of Commitment to Joint Goal changes –Status of Commitment to Attaining Joint Action in present team changes –Status of Joint Commitment of Team Member Changes Actions: R1: If status of Commitment to Joint Action changes OR Status of Commitment to Present Team Context Changes Inform all team members of change R2: If status of Joint Commitment of a team member changes Determine Whether to Continue Joint Commitment

19. Ingredients in Good Coordination 1.Have structures that enable agents to interact in predictable ways 2.Have flexibility allowing partial and imprecise viewpoint of the community (for each agent) 3.Agents must have sufficient knowledge and reasoning capabilities for exploit structure and flexibility

20. Coordination ”in a nutshell” Coordination = Commitments + Conventions + Social Conventions + Local Reasoning

21. Commitment Types Goal-Subgoal Relationships –Hierarchical, AND/OR goals Goal-Dependency Relationships –Weak/Strong dependencies –Uni/Bi-directional

22. Social Convention Types Goal-Subgoal Relationships –Believing that each individual agent will do their best to perform their subgoal Goal-Dependency Relationships –Monitoring changes in individual commitments in order to decide actions Joint Action Convention, Joint Commitments and Joint Goals  Enable individuals to make assumptions about the actions of other individuals

23. Common Coordination Techniques Organizational Structures – long term –Pattern of information and control relationships between individuals Meta-Level Information Exchange – medium term –Agents giving each other information about their current priorities and focus Multi-Agent planning – short term –Specify a plan with all future actions and interactions with respect to achieving a particular objective

24. Organizational Structures Types: –Hierarchical –Heterarchical –Flat

25. Performance of Organization Types Product Hierarchy –High Production Cost –Low Coordination Cost –High Vulnerability Cost Functional Hierarchy –Low Production Cost –Medium Coordination Cost –Very High Vulnerability Cost Centralized Market –Low Production Cost –High Coordination Cost –Quite high vulnerability Cost Decentralized Market –Low Production Cost –High Coordination Cost –Low vulnerability Cost

26. Meta-level Exchange Agents build local plans which they share with other agents in order to identify improvements in coordination Medium-term Partial Global Planning

27. Multi-Agent Planning Short-term Very high-level of detail –Everyone knows everything Two approaches –Centralized - coordinator does the planning –Distributed – agents propose plans to coordinator which does adjustments

28. Conclusions Coordination – four main structures 1.Commitments Agree on doing something in a MAS 2.Convention When to do something about commitments 3.Social Conventions Team-oriented Conventions 4.Local Reasoning Intelligence needed to fulfill conventions and commitments Related research fields –Self-organization –CSCW