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Chapter 16: Multiagent Systems

This chapter explores the architecture and functionality of multiagent systems within the context of service-oriented computing. It covers agent types, lifecycle management, and the importance of consistency maintenance in agent interactions. The discussion includes fundamental problems in multiagent systems, such as task distribution and conflict reconciliation, as well as details about agent management systems and truth maintenance systems. An emphasis is placed on the collaborative and communicative roles of agents, highlighting their capabilities and the complexities of maintaining a coherent knowledge base in distributed environments.

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Chapter 16: Multiagent Systems

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  1. Chapter 16:Multiagent Systems Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005

  2. Highlights of this Chapter • Applicability in Service-Based Systems • Multiagent Architecture • Agent Types • Lifecycle Management • Consistency Maintenance • Modeling Other Agents • Cognitive Concepts Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  3. Basic Problems of MAS • Distributing control among agents • Describing, decomposing, distributing tasks • Interacting and communicating • Representing goals, problem-solving states, and other agents • Maintaining consistency, reconciling conflicts Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  4. (de facto) Standard Agent Types Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  5. Brokerage Service • Cooperates with a Directory Service • Accepts requests from agents to recruit one or more agents who can provide a service • Uses knowledge about the requirements and capabilities of registered agents to • Identify appropriate agents for an interaction • Negotiate with selected agents • Potentially learn about the properties of the responses • Example: Brokerage determines that advertised results from agent X are incomplete and seeks a substitute for X Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  6. FIPA Agent Management System Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  7. Agent Management System: 2 • Handles the creation, registration, location, communication, migration, and retirement of agents • White pages, e.g., agent location and naming (from AMS) • Agent identifiers support social names, transport addresses, name resolution services • Yellow pages, e.g., service location and registration services (from DF) • Agent message transport services Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  8. Java Agent Development Framework JADE, a popular FIPA-compliant agent framework for multiagent systems: • http://jade.tilab.com/ • (FIPA-OS and Zeus having died) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  9. Consistency Maintenance across Services A truth maintenance system (TMS) helps maintain consistency • Performs a form of propositional deduction • Maintains justifications and explains the results of its deductions • Updates beliefs incrementally when premises change TMSs help us • Deal with atomicity • Maintain modular models Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  10. justifications Problem Solver TMS beliefs Architecture of TMS-Based Agent • Problem solver: decides on actions • TMS: maintains a network of beliefs based on the justifications relating them Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  11. Knowledge Base Integrity • Stability: believe everything justified validly; disbelieve everything else • Well-Foundedness: no circular beliefs • Logical consistency: no logical contradictions • Completeness: find a consistent state if one exists, or report failure Problems arise when knowledge is distributed Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  12. Distributed TMS • Each agent has a justification-based TMS • Each datum can have status • OUT • IN: valid local justification • EXTERNAL: must be IN for some agent • When a problem solver adds or removes a justification, the DTMS • Unlabels data based on the changed justification • Relabels all unlabeled shared data (in one or more iterations) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  13. Degrees of Logical Consistency • Inconsistency: some agent is individually inconsistent • Local Consistency: all agents are individually consistent • Local-and-Shared Consistency: agents are locally consistent and agree about any data they might share • Global Consistency: agents are globally consistent (union of KBs is consistent) The DTMS maintains local-and-shared consistency and well-foundedness Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  14. Cooperative Service: 1 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN ? recommend(?X) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN r2: recommend(X) :- takeover-bid(X) IN r1: takeover-bid(X) :- cash-rich(X) IN Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  15. Cooperative Service: 2 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN recommend(XCorp) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) IN Shared with: Client; Justification: (f2 r1 r2) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  16. Cooperative Service: 3 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN f4: recommend(xcorp) EXTERNAL Shared with: Broker; Justification: ( ) f5: buy(xcorp) IN Justification: (f3 f4 r3) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) IN Shared with: Client; Justification: (f2 r1 r2) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  17. Cooperative Service: 4 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN f4: recommend(xcorp) EXTERNAL Shared with: Broker; Justification: ( ) f5: buy(xcorp) IN Justification: (f3 f4 r3) relabel recommend(XCorp) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN --> OUT r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) IN --> OUT Shared with: Client; Justification: (f2 r1 r2) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  18. Cooperative Service: 5 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN f4: recommend(xcorp) OUT Shared with: Broker; Justification: ( ) f5: buy(xcorp) OUT Justification: (f3 f4 r3) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) OUT r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) OUT Shared with: Client; Justification: (f2 r1 r2) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  19. Chapter 16 Summary Study multiagent systems because interactions among agents make them interesting • Communication among agents is key, although markets (later chapter) only support implicit communication through prices • Programming environments support agent interactions • Consistency maintenance is a major challenge • Agents must model agents; simple techniques are often adequate; more subtle techniques can require extensive reasoning power Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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