Working Together-Multiagent Systems-Lecture Slides, Slides of Multiagent Systems

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LECTURE 9:

Working Together

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Working Together

• Why and how do agents work together?
• Important to make a distinction between:
  • benevolent agents
  • self-interested agents

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Self-Interested Agents

• If agents represent individuals or organizations, (the more general case), then we cannot make the benevolence assumption
• Agents will be assumed to act to further their own interests, possibly at expense of others
• Potential for conflict
• May complicate the design task enormously

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Task Sharing and Result

Sharing

• Two main modes of cooperative problem solving:
  • task sharing : components of a task are distributed to component agents
  • result sharing : information (partial results, etc.) is distributed

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Recognition

• In this stage, an agent recognizes it has a problem it wants help with. Agent has a goal, and either… - realizes it cannot achieve the goal in isolation — does not have capability - realizes it would prefer not to achieve the goal in isolation (typically because of solution quality, deadline, etc.)

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Announcement

• In this stage, the agent with the task sends out an announcement of the task which includes a specification of the task to be achieved
• Specification must encode:
  • description of task itself (maybe executable)
  • any constraints (e.g., deadlines, quality constraints)
  • meta-task information (e.g., “bids must be submitted by…”)
• The announcement is then broadcast

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Awarding & Expediting

• Agent that sent task announcement must choose between bids & decide who to “award the contract” to
• The result of this process is communicated to agents that submitted a bid
• The successful contractor then expedites the task
• May involve generating further manager-contractor relationships: sub-contracting

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Issues for Implementing Contract

Net

• How to…
  • …specify tasks?
  • …specify quality of service?
  • …select between competing offers?
  • …differentiate between offers based on multiple criteria?

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Cooperative Distributed Problem Solving

(CDPS)

• Neither global control nor global data storage — no agent has sufficient information to solve entire problem
• Control and data are distributed

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CDPS System Characteristics and

Consequences

• Communication is slower than computation
  • loose coupling
  • efficient protocol
  • modular problems
  • problems with large grain size

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Four Phases to Solution, as Seen in

Contract Net

1. Problem Decomposition
2. Sub-problem distribution
3. Sub-problem solution
4. Answer synthesis

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The contract net protocol deals with phase 2.

Contract Net• The collection of nodes is the “contract net”

• Each node on the network can, at different times or for different tasks, be a manager or a contractor
• When a node gets a composite task (or for any reason can’t solve its present task), it breaks it into subtasks (if possible) and announces them (acting as a manager), receives bids from potential contractors, then awards the job (example domain: network resource management, printers, …)

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Idle Node Listening to Task

Announcements

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Manager

Manager

Manager

Potential

Contractor

Node Submitting a Bid

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Manager

Potential

Contractor

Bid