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An agent is a system that is capable of independentaction on
behalf of its user or owner.
An agent is anything that can be viewed as perceiving
its environment through sensors and acting upon that
environment through effectors.
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Today, we have a distributed environment that
cannot be completely specifiedopen
environments.
Former paradigms, such as OOP, cannot
completely satisfy our needs:
They were designed for constructing systems in a
completely specified environment - a closed world.
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When a space probe makes its long flight from Earth to outer
planets, a groundcrew is usually required to continue to track its
progress and decide how to
deal with unexpected eventualities. This is costly and, if
decisions are required
quickly, it is simply not practical. For these reasons,
organisations like NASA
are seriously investigating the possibility of making the probes
more
autonomous giving them richer decision making capabilities
andresponsibilities.
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.Contains a number of agents which works acrossdifferent domains
in different enviroment bymutual coordination amongthemselves or
they work together.
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Environment
Distributed-agent System
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To solve problems that are too large for a centralized agent
To provide a solution to inherently distributed problems
To provide solutions which draw from distributed information
sources
To provide solutions where expertise is distributed
To offer conceptual clarity and simplicity of design
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Why and how do agents work
together?
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Neither global control nor global datastorage no agent has
sufficient
information to solve entire problem
Control and data are distributed
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The contract net protocol deals
with phase 2.
1.
Problem
decomposition
2.
Subproblem
solution
3.
Answer
synthesis
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Two main modes of cooperative problemsolving: task sharing:
components of a task aredistributed to component
agents
result sharing:information (partial results,
etc.) is distributed
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An approach to distributed problemsolving, focusing on task
distribution
This approach is based on companyapproach of awarding contracts
basedon tenders.
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The collection of nodes is the contract netEach node on the
network can, at different
times or for different tasks, be a manager or a
contractorWhen a node gets a composite task (or for
any reason cant solve its present task), it
breaks it into subtasks (if possible) and
announces them (acting as a manager),receives bids from
potential contractors, thenawards the job (example domain:
network
resource management, printers, )
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Different phases of Contract Net:1. Recognition
2. Announcement
3. Bidding
4. Awarding
5. Expediting
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In this stage, an agent recognizes it has aproblem 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 inisolation
(typically because of solution quality,
deadline, etc.)
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Manager
I have a
problem.
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In this stage, the agent with the task sends outan
announcementof the task which includes aspecificationof 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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Manager
Task Announcement
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Manager
Manager
Manager
Potential
Contractor
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Agents that receive the announcementdecide for themselves
whether they wishto bidfor the task
Factors: agent must decide whether it is capable ofexpediting
task
agent must determine quality constraints & price
information (if relevant) If they do choose to bid, then they
submit a
tender
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Manager
Potential
Contractor
Bid
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Manager
Potential
Contractor
PotentialContractor
Bids
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Agent that sent task announcement mustchoose between bids &
decide who toaward the contract to
The result of this process is communicatedto agents that
submitted a bid
The successful contractorthen expeditesthe task
May involve generating further manager-contractor relationships:
sub-contracting
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Manager
Contractor
Award
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Suitable for domains that can be viewed in
terms of tasks
Disadvantages Doesnt detect conflicts
Assumes benevolent agents
Communication intensive
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