Sisteme multi-agent

Universitatea “Politehnica” din Bucurestianul universitar 2005-2006Adina Magda Floreaadina@cs.pub.ro

http://turing.cs.pub.ro/blia_06

Curs 1Curs 1 Motivatie pentru agenti Definitii agenti Sisteme multi-agent Inteligenta agentilor Sub-domenii de cercetare

De ce agenti?De ce agenti? Sisteme complexe, pe scara larga,

distribuite Sisteme deschise si heterogene –

construirea independenta a componentelor Distributia resurselor Distributia expertizei Personalizare Interoperabilitatea sistemelor/ integrare

legacy systems3

Agent?Agent?Termenul agent este frecvent utilizat in:

• Sociologie, biologie, psihologie cognitiva, psihologie sociala si

• Stiinta calculatoarelor IA Ce sunt agentii? Ce sunt agentii in stiinta calculatoarelor? Aduc ceva nou? Cum difera agentii software de alte programe?

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Definitii ale agentilor in stiinta Definitii ale agentilor in stiinta calculatoarelorcalculatoarelor

Nu exista o definitie unanim acceptata De ce este greu de definit? IA, agenti inteligenti, sisteme multi-agent Aparent agentii sunt dotati cu inteligenta Sunt toti agentii inteligenti? Agent = definit mai mult prin caracteristici,

unele pot fi considerate ca manifestari ale unui comportament inteligent

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Definitii agentiDefinitii agenti

“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)

“An agent is an entity that senses its environment and acts upon it” (Russell, 1997)

“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)”

“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;

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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Caracteristici identificateCaracteristici identificate2 directii de definitie Definirea unui agent izolat Definirea agentilor in colectivitate

dimensiune sociala SMA

2 tipuri de definitii Nu neaparat agenti inteligenti Include o comportare tipica IA agenti

inteligenti9

Caracteristici agenti Actioneaza pentru un utilizator sau un program Autonomie Percepe mediul si actioneaza asupra lui reactiv Actiuni pro-active

goal-directed behavior vs reactive behaviour?goal-directed behavior vs reactive behaviour? Caracter social Functionare continua (persistent software) mobilitate ?

inteligenta?inteligenta? Scopuri, rationalitate Rationament, luarea deciziilor cognitivcognitiv Invatare/adaptare Interactiune cu alti agenti – dimensiune sociala

Alte moduri de a realiza inteligenta?10

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Mediul agentului

Agent

Mediu

Sensorintrare

Actiuneiesire

Proprietatile mediului

- Accesibil vs inaccesibil

- Determinist vs nondeterminist

- Episodic vs non-episodic

- Static vs dinamic

- Deschis vs inchis

- Contine sau nu alti agenti

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Exemple de agenti?Exemple de agenti?Agenti inteligenti?Agenti inteligenti?

Thermostat Calendar electronic Lista emails Sistem de control al traficului aerian

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Exemple de agentiExemple de agentiButtler agentButtler agent

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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NASA agentsNASA agents 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.

NASA’s Earth Observing-1 satellite, which began operation in 2000, was recently turned into an autonomous agent testbed.Image Credit: NASA

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Robocup agentsRobocup agents 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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SwarmsSwarms Intelligent Small World Autonomous Robots for Micro-manipulation

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 SolutionsIntelligent 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 AutonomyTrue UAV Autonomy 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.

Sisteme multi-agentSisteme multi-agentMai multi agenti intr-un mediu comun

Mediu

Zona de influenta Interactiuni 19

Interactiuni intre agenti- nivel inalt

Interactiuni pentru- coordonare- comunicare- organizare

Coordonare motivati colectiv motivati individual

- scopuri proprii / indiferenta- scopuri proprii / competitie pentru resurse- scopuri proprii si contradictorii / competitie pentru resurse- scopuri proprii / coalitii

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SMA – mai multi agenti in acelasi mediuSMA – mai multi agenti in acelasi mediu

Comunicare protocol limbaj

- negociere- ontologii Structuri organizationale

centralizate vs decentralizate

ierarhie/ piataabordare "agent cognitiv""agent cognitiv"

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How do agents acquire intelligence?Cognitive agentsThe 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 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 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.

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 Simple processing units that perceive and react to changes

in their environment. Do not have a symbolic representation of the world and do

not use complex symbolic reasoning. 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 problem of Prisoner's DilemmaOutcomes 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.

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

Player A / Player B Defect Cooperate

Defect 2 , 2 5 , 0

Cooperate 0 , 5 3 , 3

The problem of pray and predators

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Reactive approachThe preys emit a signal whose intensity decreases in proportion to distance - plays the role of attractor for the predatorsHunters emit a signal which acts as a repellent for other hunters, so as not to find themselves at the same placeEach hunter is each attracted by the pray and (weakly) repelled by the other hunters

Cognitive approachDetection of prey animalsSetting up the hunting team; allocation of rolesReorganisation of teamsNecessity for dialogue/communication and for coordinationPredator agents have goals, they appoint a leader that organize the distribution of work and coordinate actions

Is intelligence the only optimal action towards a a goal? Only rational behaviour?

Emotional agents A computable science of emotions Virtual actors

– Listen trough speech recognition software to people– Respond, in real time, with morphing faces, music, text, and speech

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

Manifest temperament control of emotions27

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Decision theory

Economictheories

Sociology

Psychology

Distributedsystems

OOP

Artificial intelligenceand DAI

AutonomyMarkets

LearningProactivity

Reactivity

Cooperation

Character

Communication

Mobility

Organizations

AOP

MAS

MAS links with other disciplines

Rationality

Areas of R&D in MASAreas of R&D in MAS

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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

Areas of R&D in MASAreas 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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