Download Multi-Agent Systems

Multi-Agent Systems
University “Politehnica” of Bucarest
Spring 2010
Adina Magda Florea
http://turing.cs.pub.ro/mas_10
curs.cs.pub.ro
Course goals
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Multi-agent systems (MAS) may be viewed as a
collection of distributed autonomous artifacts capable
of accomplishing complex tasks through interaction,
coordination, collective intelligence and emergence of
patterns of behavior.
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By the end of this course, you will know:
– what are the basic ideas, models, and paradigms
offered by intelligent agents and MAS;
– build multi-agent systems or select the right MAS
framework for solving a problem
– use the agent technology in different areas of
applications
– what do agents bring as compared to distributed
processing or object oriented software development.
Course content
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What are agents and MAS?
Agent architectures
Communication
Knowledge representation
Distributed planning
Coordination
Auctions
Negotiation
Agent oriented programming
MAS learning
Agents and web services
Agents and MAS applications
Course requirements
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Course grades
Mid-term exam
Final exam
Projects
Laboratory
20%
30%
30%
20%
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Requirements: min 7 lab attendances, min 50% of
term activity (mid-term ex, projects, lab)
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Academic Honesty Policy
It will be considered an honor code violation to give
or use someone else's code or written answers,
either for the assignments or exam tests. If such a
case occurs, we will take action accordingly.
Lecture 1: Introduction
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Motivation for agents
Definitions of agents  agent
characteristics, taxonomy
Agents and objects
Multi-Agent Systems
Agent’s intelligence
Areas of R&D in MAS
Exemplary application domains
Motivations for agents
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Large-scale, complex, distributed systems:
understand, built, manage
Open and heterogeneous systems - build
components independently
Distribution of resources
Distribution of expertise
Needs for personalization and customization
Interoperability of pre-existing systems /
integration of legacy systems
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Agent?
The term agent is used frequently nowadays in:
• Sociology, Biology, Cognitive Psychology, Social
Psychology, and
• Computer Science  AI
 Why agents?
 What are they in Computer Science?
 Do they bring us anything new in modelling and
constructing our applications?
 Much discussion of what (software) agents are and of how
they differ from programs in general
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What is an agent (in computer
science)?
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There is no universally accepted definition of the term agent and there
is a good deal of ongoing debate and controversy on this subject
The situation is somehow comparable with the one encountered when
defining artificial intelligence.
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Why was it so difficult to define artificial intelligence (and we still doubt
that we have succeeded in giving a proper definition) and
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Why is it so difficult to define agents and multi-agent systems, when
some other concepts in computer science, such as object-oriented,
distributed computing, etc., were not so resistant to be properly
defined.
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The concept of agent, as the one of artificial intelligence, steams from
people, from the human society. Trying to emulate or simulate human
specific concepts in computer programs is obviously extremely difficult
and resist definition.
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More than 30 years ago, computer scientists set
themselves to create artificial intelligence
programs to mimic human intelligent behaviour,
so the goal was to create an artefact with the
capacities of an intelligent person.
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Now we are facing the challenge to emulate or
simulate the way human act in their
environment, interact with one another,
cooperatively solve problems or act on behalf
of others, solve more and more complex
problems by distributing tasks or enhance
their problem solving performances by
competition.
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It appears that the agent paradigm is one
necessarily endowed with intelligence.
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Are all computational agents intelligent?
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The answer may be as well yes as no.
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Not to enter a debate about what
intelligence is
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Agent = more often defined by its
characteristics - many of them may be
considered as a manifestation of some
aspect of intelligent behaviour.
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Agent definitions
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“Most often, when people use the term ‘agent’
they refer to an entity that functions
continuously and autonomously in an
environment in which other processes take
place and other agents exist.” (Shoham,
1993)
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“An agent is an entity that senses its
environment and acts upon it” (Russell,
1997)
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“Intelligent agents continuously perform three
functions: perception of dynamic conditions in the
environment; action to affect conditions in the
environment; and reasoning to interpret
perceptions, solve problems, draw inferences, and
determine actions. (Hayes-Roth 1995)”
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“Intelligent agents are software entities that carry
out some set of operations on behalf of a user or
another program, with some degree of
independence or autonomy, and in so doing,
employ some knowledge or representation of the
user’s goals or desires.” (the IBM Agent)
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“Agent = a hardware or (more usually) a software-based
computer system that enjoys the following properties:
 autonomy - agents operate without the direct intervention
of humans or others, and have some kind of control over
their actions and internal state;
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Flexible autonomous action
 reactivity: agents perceive their environment and respond
in a timely fashion to changes that occur in it;
 pro-activeness: agents do not simply act in response to
their environment, they are able to exhibit goal-directed
behaviour by taking initiative.”
 social ability - agents interact with other agents (and
possibly humans) via some kind of agent-communication
language;
(Wooldridge and Jennings, 1995)
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Identified characteristics
Two main streams of definitions
 Define an agent in isolation
 Define an agent in the context of a society of
agents  social dimension  MAS
Two types of definitions
 Does not necessary incorporate intelligence
 Must incorporate a kind of IA behaviour 
intelligent agents
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Agents characteristics
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act on behalf of a user or a / another program
autonomous
sense the environment and acts upon it / reactivity
purposeful action / pro-activity
goal-directed behavior vs reactive behaviour?
function continuously / persistent software
mobility ?
intelligence?
Goals, rationality
Reasoning, decision making
cognitive
Learning/adaptation
Interaction with other agents - social dimension
Other basis for intelligence?
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Questions: Examples of agents?
(are they all agents?) Intelligent?
 a thermostat with a sensor for detecting room
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temperature
electronic calendar
log-in into your computer; you are presented with a list
of email messages sorted by date
log-in into your computer; you are presented with a list
of email messages sorted by order of importance
air-traffic control system of country X fails - air-traffic
controls in the neighboring countries deal with
affected flights
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Agent Environment
Environment properties
- Accessible vs inaccessible
Agent
- Deterministic vs
nondeterministic
Sensor
Input
Action
Output
- Episodic vs non-episodic
- Static vs dynamic
Environment
- Open vs closed
- Contains or not other agents
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Multi-agent systems
Many entities (agents) in a common
environment
Environment
Influenece area
Interactions
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MAS - many agents in the same environment
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Interactions among agents
- high-level interactions
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Interactions for
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Coordination
- coordination
- communication
- organization
 collectively motivated / interested
 self interested
- own goals / indifferent
- own goals / competition / competing for the same resources
- own goals / competition / contradictory goals
- own goals / coalitions
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Communication
 communication protocol
 communication language
- negotiation to reach agreement
- ontology
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Organizational structures
 centralized vs decentralized
 hierarchical/ markets
"cognitive agent" approach
MAS systems?
 Electronic calendars
 Air-traffic control system
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Agents vs Objects
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Autonomy - stronger - agents have sole control over their
actions, an agent may refuse or ask for compensation
Flexibility - Agents are reactive, like objects, but also proactive
Agents are usually persistent
Own thread of control
Agents vs MAS
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Coordination - as defined by designer, no contradictory
goals
Communication - higher level communication than object
messages
Organization - no explicit organizational structures for
objects
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No prescribed rational/intelligent behaviour
How do agents acquire intelligence?
Cognitive agents
The model of human intelligence and human perspective of
the world  characterise an intelligent agent using
symbolic representations and mentalistic notions:
 knowledge - John knows humans are mortal
 beliefs - John took his umbrella because he believed it was going to
rain
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desires, goals - John wants to possess a PhD
intentions - John intends to work hard in order to have a PhD
choices - John decided to apply for a PhD
commitments - John will not stop working until getting his PhD
obligations - John has to work to make a living
(Shoham, 1993)
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Premises
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Such a mentalistic or intentional view of agents - a kind of
"folk psychology" - is not just another invention of computer
scientists but is a useful paradigm for describing complex
distributed systems.
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The complexity of such a system or the fact that we can not
know or predict the internal structure of all components
seems to imply that we must rely on animistic, intentional
explanation of system functioning and behavior.
Is this the only way agents can acquire intelligence?
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Comparison with AI - alternate approach of realizing intelligence - the
sub-symbolic level of neural networks
An alternate model of intelligence in agent systems.
Reactive agents
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Simple processing units that perceive and react to changes
in their environment.
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Do not have a symbolic representation of the world and do
not use complex symbolic reasoning.
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The advocates of reactive agent systems claims that
intelligence is not a property of the active entity but it is
distributed in the system, and steams as the result of the
interaction between the many entities of the distributed
structure and the environment.
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The wise men problem
A king wishing to know which of his three wise men is the wisest,
paints a white spot on each of their foreheads, tells them at least one
spot is white, and asks each to determine the color of his spot. After
a while the smartest announces that his spot is white
The problem of Prisoner's Dilemma
Outcomes for actor A (in hypothetical "points") depending on the combination of
A's action and B's action, in the "prisoner's dilemma" game situation. A similar
scheme applies to the outcomes for B.
Player A / Player B
Defect
Cooperate
Defect
2,2
5,0
Cooperate
0,5
3,3
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The problem of pray and predators
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Cognitive approach
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Detection of prey animals
Setting up the hunting team; allocation of roles
Reorganisation of teams
Necessity for dialogue/communication and for coordination
Predator agents have goals, they appoint a leader that organize the
distribution of work and coordinate actions
Reactive approach
The preys emit a signal whose intensity decreases in proportion to
distance - plays the role of attractor for the predators
Hunters emit a signal which acts as a repellent for other hunters, so
as not to find themselves at the same place
Each hunter is each attracted by the pray and (weakly) repelled by the
other hunters
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Is intelligence the only optimal action towards a a goal? Only rational
behaviour?
Emotional agents
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A computable science of emotions
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Virtual actors
– Listen trough speech recognition software to people
– Respond, in real time, with morphing faces, music, text, and speech
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Emotions:
– Appraisal of a situation as an event: joy, distress;
– Presumed value of a situation as an effect affecting another: happy-for,
gloating, resentment, jealousy, envy, sorry-for;
– Appraisal of a situation as a prospective event: hope, fear;
– Appraisal of a situation as confirming or disconfirming an expectation:
satisfaction, relief, fears-confirmed, disappointment
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Manifest temperament control of emotions
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MAS links with other disciplines
Economic
theories
Decision theory
OOP
AOP
Distributed
systems
Markets
Autonomy
Rationality
Communication
MAS
Mobility
Learning
Proactivity
Cooperation
Organizations
Character
Sociology
Reactivity
Artificial intelligence
and DAI
Psychology
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Areas of R&D in MAS
 Agent architectures
 Knowledge representation: of world, of itself, of the
other agents
 Communication: languages, protocols
 Planning: task sharing, result sharing, distributed
planning
 Coordination, distributed search
 Decision making: negotiation, markets, coalition
formation
 Learning
 Organizational theories
 Norms
 Trust and reputation
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Areas of R&D in MAS
 Implementation:
– Agent programming: paradigms, languages
– Agent platforms
– Middleware, mobility, security
 Applications
– Industrial applications: real-time monitoring and management
of manufacturing and production process, telecommunication
networks, transportation systems, electricity distribution
systems, etc.
– Business process management, decision support
– eCommerce, eMarkets
– Information retrieving and filtering
– Human-computer interaction
– CAI, Web-based learning
- CSCW
– PDAs
- Entertainment
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Agents in action
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NASA’s Earth Observing-1 satellite, which began operation in
2000, was recently turned into an autonomous agent testbed.
Image Credit: NASA
NASA uses autonomous agents to handle tasks that appear
simple but are actually quite complex. For example, one mission
goal handled by autonomous agents is simply to not waste fuel.
But accomplishing that means balancing multiple demands,
such as staying on course and keeping experiments running, as
well as dealing with the unexpected.
"What happens if you run out of power and you're on the dark
side of the planet and the communications systems is having a
problem? It's all those combinations that make life exciting,"
says Steve Chien, principal scientist for automated planning and
scheduling at the NASA Jet Propulsion Laboratory in Pasadena,
Calif.
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TAC SCM
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Negotiation was one of the key agent capabilities tested at the
conference's Trading Agent Competition. In one contest,
computers ran simulations of agents assembling PCs. The
agents were operating factories, managing inventories,
negotiating with suppliers and buyers, and making decisions
based on a range of variables, such as the risk of taking on a
big order even if all the parts weren't available. If an agent made
an error in judgment, the company could face financial penalties
and order cancellations.
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Exemple de agenti
Buttler agent
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Imagine your very own mobile butler, able to
travel with you and organise every aspect of
your life from the meetings you have to the
restaurants you eat in.
The program works through mobile phones
and is able to determine users' preferences
and use the web to plan business and social
events
And like a real-life butler the relationship
between phone agent and user improves as
they get to know each other better.
The learning algorithms will allow the butler to
arrange meetings without the need to consult
constantly with the user to establish their
requirements.
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Robocup agents
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The goal of the annual RoboCup competitions,
which have been in existence since 1997, is to
produce a team of soccer-playing robots that
can beat the human world champion soccer
team by the year 2050.
http://www.robocup.org/
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Swarms
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Intelligent Small World Autonomous Robots for Micromanipulation
A leap forward in robotics research by combining experts in microrobotics, in
distributed and adaptive systems as well as in self-organising biological
swarm systems.
Facilitate the mass-production of microrobots, which can then be employed as
a "real" swarm consisting of up to 1,000 robot clients. These clients will all be
equipped with limited, pre-rational on-board intelligence.
The swarm will consist of a huge number of heterogeneous robots, differing in
the type of sensors, manipulators and computational power. Such a robot
swarm is expected to perform a variety of applications, including micro
assembly, biological, medical or cleaning tasks.
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Intelligent IT Solutions
Goal-Directed™ Agent technology.
AdaptivEnterprise™ Solution Suite
allow businesses to migrate
from traditionally static,
hierarchical organizations to
dynamic, intelligent distributed
organizations capable of
addressing constantly changing
business demands.
Supports a large number of
variables, high variety and
frequent occurrence of
unpredictable external events.
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True UAV Autonomy
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In a world first, truly autonomous, Intelligent
Agent-controlled flight was achieved by a
Codarra ‘Avatar’ unmanned aerial vehicle
(UAV).
The flight tests were conducted in restricted
airspace at the Australian Army’s Graytown
Range about 60 miles north of Melbourne.
The Avatar was guided by an on-board
JACK™ intelligent software agent that
directed the aircraft’s autopilot during the
course of the mission.
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Information agents
Personal agents (PDA)
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provide "intelligent" and user-friendly interfaces
observe the user and learn user’s profile
sort, classify and administrate e-mails,
organize and schedule user's tasks
in general, agents that automate the routine tasks of the
users
Web agents
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Tour guides
Indexing agents
FAQ finders
Expertise finder
Search engines
- human indexing
- spider indexing
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Agents in eLearning
Agents’ role in e-learning
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Enhance e-learning content and experience
 give help, advice, feedback
 act as a peer learning
 participate in assessments
 participate in simulation
 personalize the learning experience
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Enhance LMSs
 facilitate participation
 facilitate interaction
 facilitate instructor’s activities
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Agents for e-Commerce
E-commerce
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Transactions
- business-to-busines (B2B)
- business-to-consumer (B2C)
- consumer-to-consumer (C2C)
Difficulties of eCommerce
 Trust
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Privacy and security
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Billing
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Reliability
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