Chapter 16: Multiagent Systems

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