CPE/CSC 580:
Intelligent Agents
Franz J. Kurfess
Computer Science Department
California Polytechnic State University
San Luis Obispo, CA, U.S.A.
1
Course Overview
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Introduction
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Intelligent Agent, Multi-Agent Systems
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Agent Examples
Agent Architectures
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Reasoning Agents
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Agent Encounters, Resource Sharing, Agreements
Communication
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Observation, Analysis, Performance Improvement
Multi-Agent Interactions
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Knowledge, Reasoning, Planning
Learning Agents
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Agent Hierarchy, Agent Design Principles
Speech Acts, Agent Communication Languages
Collaboration
© Franz J. Kurfess
3
Overview Collaboration
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Motivation
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Objectives
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Collaboration
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Cooperative Distributed Problem Solving
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self-interest, societal benefits
Benevolent vs. Self-interested Agents
Task Sharing and Result Sharing
Contract Net for Task Allocation
Blackboards
Example: HEARSAY II
Important Concepts and Terms
© Franz J. Kurfess
4
Collaboration
Benevolent vs. Self-interested
Agents
Task Sharing and Result Sharing
Contract Net for Task Allocation
10
Benevolent Agents
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agents help each other whenever ask
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within “reasonable” limits
Cooperative Distributed Problem Solving (CDPS)
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systems consisting of benevolent agents
much easier to design than non-benevolent systems
possible if the whole system has a single owner or designer
© Franz J. Kurfess
11
Self-Interested Agents
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agents representing individuals or organizations
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always consider their interest first
may come at the expense of others
potential for conflict
more general
more difficult to design systems
self-interested agents are not necessarily malevolent
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no intention to harm other agents
© Franz J. Kurfess
12
Cooperative Problem Solving
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task sharing
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components of a task are distributed to participating agents
result sharing
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information is distributed
may be intermediate or partial results
© Franz J. Kurfess
13
Contract Net
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task-sharing protocol for task allocation among agents
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recognition
announcement
bidding
awarding
expediting
© Franz J. Kurfess
14
Recognition
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agent realizes that it needs help with a problem
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goal can not be achieve in isolation
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agent does not have the necessary capabilities
agent prefers to achieve in collaboration with others
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better solution quality
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resource utilization
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risk
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deadline
© Franz J. Kurfess
15
Announcement
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agent sends out a task announcement
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specification of the task to be achieved
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task description
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“delivery of a component to location A”
constraint
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deadline
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quality
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handling
meta-information
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housekeeping
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deadline for bids
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format for bids
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payment modalities
© Franz J. Kurfess
16
Bidding
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recipients of the announcement decide if they want to
bid for the task
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capabilities
capacities
quality constraints
price information
agents that choose to bid submit a tender
© Franz J. Kurfess
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Awarding
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originating agent selects bid and awards the contract
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winning bidder is notified and awarded the contract
other bidding agents are notified
“contractor” expedites the task
may lead to further tasks to be distributed
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“sub-contracting”
© Franz J. Kurfess
18
Contract Net Example
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task announcement
bidding
award
contract
[Woolridge 2009]
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Node Issues Task Announcement
Task Announcement
Manager
[Woolridge 2009]
9-18
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Idle Node Listening to Task
Announcements
Manager
Potential
Contractor
Manager
Manager
[Woolridge 2009]
9-19
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Node Submitting a Bid
Bid
Manager
Potential
Contractor
[Woolridge 2009]
9-20
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Manager Listening to Bids
Bids
Potential
Contractor
Manager
Potential
Contractor
[Woolridge 2009]
9-21
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Manager Making an Award
Award
Manager
Contractor
[Woolridge 2009]
9-22
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Contract Established
Contract
Manager
Contractor
[Woolridge 2009]
9-23
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Contract Net Issues
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task specification
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quality of service
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selection between competing offers
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may require balancing multiple criteria
© Franz J. Kurfess
26
Cooperative Distributed
Problem Solving
(CDPS)
Basics of CDPS
CDPS and Contract Nets
Blackboards
Example: HEARSAY II
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Cooperative Distributed Problem Solving
(CDPS)
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distributed control
distributed data storage
no agent has sufficient information to
solve the entire problem
[Woolridge 2009]
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CDPS System Characteristics
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Assumption: Communication is slower than
computation
loose coupling
 efficient protocol
 modular problems
 problems with large grain size
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[Woolridge 2009]
9-14
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CDPS System Consequences
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any unique node is a potential bottleneck
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distribute data
 distribute control
organized behavior is hard to
guarantee
 no one node has the complete picture

[Woolridge 2009]
9-15
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CDPS Phases
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Problem Decomposition
Sub-problem distribution
Sub-problem solution
Answer synthesis
The contract net protocol deals with phase 2, subproblem distribution.
9-16
[Woolridge 2009]
31
Contract Net for CDPS
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collection of nodes is the “contract net”
each node on the network can be a manager or a
contractor
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at different times
for different tasks,
sub-contracting
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a node gets a composite task or can’t solve its present
task
breaks it into subtasks
announces subtasks
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acting as a manager
receives bids from potential contractors
awards the job
[Woolridge 2009]
9-17
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Blackboard Systems
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design for distributed collaborative systems
central area that serves as a task sharing
message board
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“blackboard” (BB)
no relation to the Blackboard course management
system
reasonably efficient implementation of a
DCPS
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blackboard may be a bottleneck
[Woolridge 2009]
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Result Sharing in Blackboard Systems
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first scheme for cooperative problem solving
results shared via shared data structure (BB)
multiple agents can read and write to BB
agents write partial solutions to BB
BB may be structured into hierarchy
mutual exclusion over BB required ⇒
bottleneck
limitations on concurrent activities
Compare: LINDA tuple spaces, JAVASPACES
[Woolridge 2009]
34
Hearsay II Speech Understanding
System
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developed at Carnegie-Mellon in the mid1970’s
goal was to reliably interpret connected
speech involving a large vocabulary
first example of the blackboard architecture,
“a problem-solving organization that can
effectively exploit a multi-processor system.”
(Fennel and Lesser, 1976)
required a distributed system architecture
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too challenging for single computers
[Woolridge 2009]
9-27
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Summary Collaboration
© Franz J. Kurfess
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Important Concepts and
Terms
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agent
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benevolent
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blackboard competition
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collaboration
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contract net
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coordination
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Cooperative Distributed Problem Solving (CDPS)
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multi-agent system
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result sharing
© Franz J. Kurfess
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