1. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
Chapter 16: Multiagent Systems
Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005
© Singh & Huhns

2. Highlights of this Chapter
Service-Oriented Computing: Semantics, Processes, Agents
August 2004
Highlights of this Chapter
Applicability in Service-Based Systems
Multiagent Architecture
Agent Types
Lifecycle Management
Consistency Maintenance
Modeling Other Agents
Cognitive Concepts
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

3. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

4. (de facto) Standard Agent Types
Service-Oriented Computing: Semantics, Processes, Agents
August 2004
(de facto) Standard Agent Types
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & 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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

6. FIPA Agent Management System
Chapter 16
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
Chapter 16
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:
(FIPA-OS and Zeus having died)
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

9. Consistency Maintenance across Services
Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

10. Architecture of TMS-Based Agent
Service-Oriented Computing: Semantics, Processes, Agents
August 2004
Architecture of TMS-Based Agent
Problem
Solver
TMS
justifications
beliefs
Problem solver: decides on actions
TMS: maintains a network of beliefs based on the justifications relating them
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

11. Knowledge Base Integrity
Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

12. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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)
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

13. Degrees of Logical Consistency
Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

14. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

15. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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)
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

16. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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)
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

17. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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)
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

18. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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)
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns

19. Service-Oriented Computing: Semantics, Processes, Agents
August 2004
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
Chapter 16
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns
© Singh & Huhns