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Chapter 16: Multiagent Systems. Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005. Highlights of this Chapter. Applicability in Service-Based Systems Multiagent Architecture Agent Types Lifecycle Management

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Chapter 16: Multiagent Systems


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chapter 16 multiagent systems
Chapter 16:Multiagent Systems

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

highlights of this chapter
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

basic problems of mas
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

de facto standard agent types
(de facto) Standard Agent Types

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

brokerage service
Brokerage Service
  • Cooperates with a Directory Service
  • An agent requests the Brokerage Service to recruit one or more agents who can provide a service
  • Brokerage Service uses knowledge about the requirements and capabilities of registered agents to
    • Determine the appropriate agents to which to forward a request for a service
    • Negotiates with the agents to determine a suitable set of service providers
    • Potentially learn about the properties of the responses
      • example: Brokerage agent 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

fipa agent management system
FIPA Agent Management System

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

agent management system 2
Agent Management System: 2
  • Handles the creation, registration, location, communication, migration and retirement of agents. Provides the following services:
    • White pages, such as agent location, naming and control access services, which are provided by the Agent Management System (AMS). Agent names are represented by a flexible and extensible structure called an agent identifier, which can support social names, transport addresses, name resolution services, amongst other things
    • Yellow pages, such as service location and registration services, which are provided by the Directory Facilitator (DF)
    • Agent message transport services

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

j ava a gent de velopment framework
Java Agent Development Framework

JADE, the most popular FIPA-compliant agent framework for multiagent systems:

  • http://jade.tilab.com/
  • The most established of the publicly available agent frameworks
  • (FIPA-OS and Zeus having died)

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

consistency maintenance across services
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

architecture of tms based agent

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

knowledge base integrity
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

distributed tms
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

degrees of logical consistency
Degrees of Logical Consistency
  • Inconsistency: an 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

cooperative service 1
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

cooperative service 2
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

cooperative service 3
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

cooperative service 4
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

cooperative service 5
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

chapter 16 summary
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