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Introduction to Intelligent Agents
Jacques Robin
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Outline What are intelligent agents?
Characteristics of artificial intelligence Applications and sub-fields of artificial intelligence Characteristics of agents Characteristics of agents’ environments Agent architectures
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What are Intelligent Agents?
Q: What are Software Agents? A: Software which architecture is based on the following abstractions: Immersion in a distributed environment, continuous thread, encapsulation, sensor, perception, actuator, action, own goal, autonomous decision making Q: What is Artificial Intelligence? A: Field of study dedicated to: Reduce the range of tasks that humans carry out better than current software or robots Emulate humans’ capability to solve approximately but efficiently most instances of problems proven (or suspected) hard to solve algorithmically (NP-Hard, Undecidable etc.) in the worst case, using innovative, often human inspired, alternative computational metaphors and techniques Emulate humans’ capability to solve vaguely specified problems using partial, uncertain information Artificial Intelligence Agents Distributed Systems Software Engineering
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Artificial Intelligence: Characteristics
Highly multidisciplinary inside and outside computer science Ran-away field - by definition - at the forefront of computation tackling ever more innovative, challenging problems as the one it solved become mainstream computing Most research in any other field of computation also involves AI problems, techniques, metaphors Q: What conclusions can be derived from these characteristics? A: Hard to avoid; very, very hard to do well “Well” as in: Well-founded (rigorously defined theoretical basis, explicit simplifying assumptions and limitations) Easy to use (seamlessly integrated, easy to understand) Easy to reuse (general, extendable techniques) Scalable (at run time, at development time)
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What is an Agent? General Minimal Definition
Any entity (human, animal, robot, software): Situated in an environment (physical, virtual or simulated) that Perceives the environment through sensors (eyes, camera, socket) Acts upon the environment through effectors (hands, wheels, socket) Possess its own goals, i.e., preferred states of the environments (explicit or implicit) Autonomously chooses its actions to alter the environment towards its goals based on its perceptions and prior encapsulated information about the environment Processing cycle: Use sensor to perceive P Interprets I = f(P) Chooses the next action A = g(I,G) to perform to reach its goal G Use actuator to execute A
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What is an Agent? Agent Environment Perception
Interpretation: I = f(P) P Environment percepts Self-percepts Communicative percepts Sensors Goals Action Choice: A = g(I,O) Autonomous Reasoning Environment altering actions Perceptive actions Communicative actions A Effectors
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Agent x Object Intentionality: Encapsulate own goals (even if implicitly) in addition to data and behavior Decision autonomy: Pro-actively execute behaviors to satisfy its goals Can negate request for execution of a behavior from another agent More complex input/output: percepts and actions Temporal continuity: encapsulate an endless thread that constantly monitors the environment Coarser granularity: Encapsulate code of size comparable to a package or component Composed of various objects when implemented using an OO language No goal No decision autonomy: Execute behaviors only reactively whenever invoked by other objects Always execute behavior invoked by other objects Simpler input/output: mere method parameters and return values Temporally discontinuous: active only during the execution of its methods
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Intelligent Agent x Simple Software Agent
Environment Sensors Effectors Goals Percept Interpretation: I = f(P) Action Choice: A = g(I,O) Conventional Processing AI
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Classical AI System Intelligent Agent Situated Agent Disembodied AI
Environment Sensors Effectors Goals Percept Interpretation Action Choice AI Situated Agent Reasoning Input Data Output Data Goal Disembodied AI System
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What is an Agent? Other Optional Properties
Reasoning Autonomy: Requires AI, inference engine and knowledge base Key for: embedded expert systems, intelligent controllers, robots, games, internet agents ... Adaptability: Requires IA, machine learning Key for: internet agents, intelligent interfaces, ... Sociability: Requires AI + advanced distributed systems techniques: Standard protocols for communication, cooperation, negotiation Automated reasoning about other agents’ beliefs, goals, plans and trustfulness Social interaction architectures Key for: multi-agent simulations, e-comerce, ...
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What is an Agent? Other Optional Properties
Personality: Requires AI, attitude and emotional modeling Key for: Digital entertainment, virtual reality avatars, user-friendly interfaces ... Temporal continuity and persistence: Requires interface with operating system, DBMS Key for: Information filtering, monitoring, intelligent control, ... Mobility: Requires: Network interface Secure protocols Mobile code support Key for: information gathering agents, ... Security concerns prevented its adoption in practice
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Welcome to the Wumpus World!
Agent-Oriented Formulation: Agents: gold digger Environment objects: caverns, walls, pits, wumpus, gold, bow, arrow Environment’s initial state Agents’ goals: be alive cavern (1,1) with the gold Perceptions: Touch sensor: breeze, bump Smell sensor: stench Light sensor: glitter Sound sensor: scream Actions: Legs effector: forward, rotate 90º Hands effector: shoot, climb out
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Wumpus World: Abbreviations
1 2 3 4 start S A B P W S, B, G G A - Agent W - Wumpus P - Pit G - Gold X? – Possibly X X! – Confirmed X V – Visited Cavern B – Breeze S – Stench G – Glitter OK – Safe Cavern
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Perceiving, Reasoning and Acting in the Wumpus World
Percept sequence: nothing breeze Wumpus world model maintained by agent: 1 2 3 4 A ok 1 2 3 4 ok A V P? b t=0 t=2
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Perceiving, Reasoning and Acting in the Wumpus World
Percept sequence: stench {stench, breeze, glitter} Wumpus World Model: 1 2 3 4 ok A V b W! s P! 1 2 3 4 ok A S V b P! W! S B G P? Action Sequence: t=11: Go to (2,3) to find gold t=7: Go to (2,1), Sole safe unvisited cavern
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Classification Dimensions of Agent Environments
Agent environments can be classified as points in a multi-dimensional spaces The dimensions are: Observability Determinism Dynamicity Mathematical domains of the variables Episodic or not Multi-agency Size Diversity
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Observability Fully observable (or accessible):
Agent sensors perceive at each instant all the aspects of the environment relevant to choose best action to take to reach goal Partially observable (or inaccessible, or with hidden variables) Sources of partial observability: Realm inaccessible to any available sensor Limited sensor scope Limited sensor sensitivity Noisy sensors
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Determinism Deterministic: all occurrence of executing a given action in a given situation always yields same result Non-deterministic (or stochastic): action consequences partially unpredictable Sources of non-determinism: Inherent to the environment: quantic granularity, games with randomness Other agents with unknown or non-deterministic goal or action policy Noisy effectors Limited granularity of effectors or of the representation used to choose the actions to execute
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Dynamicity: Static and Sequential Environments
Static: Single perception-reasoning-action cycle during which environment is static Sequential: Sequence of perception-reasoning-action cycles during each of which the environment changes only as a result of the agent’s actions Static Environment State 1 State 2 Agent Reasoning Percept Ação ... Sequential Environment State 1 State 2 State 3 State N Agent Reasoning Reasoning Reasoning Percept Action Percept Action Percept Ação
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Dynamicity: Concurrent Synchronous and Asynchronous
Synchronous: Environment can change on its own between one action and the next perception of an agent, but not during its reasoning Asynchronous: Environment can change on its own at any time, including during the agent’s reasoning ... Percept Synchronous Concurrent Environment Agent Action State 1 Reasoning State 2 State 4 State 5 State 3 ... Percept Asynchronous Concurrent Environment Agent Action State 1 Reasoning State 2 State 4 State 3 State 5 State 6
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Dynamicity: Stationary and Non-Stationary
Stationary: The underlying laws or rules that govern state changes in the environment are fixed and immutable; they remain the same during the entire lifetime of the agent ex, a soccer game is asynchronous, yet stationary Non-Stationary: The underlying laws or rules that govern state changes in the environment are themselves subject to dynamic changes (meta-level changes) during the lifetime of the agent ex, an accounting agent acts in a non-stationary environment, since the tax laws are subject to changes from one year to the next
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Multi-Agency Sophistication of agent society: Main classes:
Number of agent roles and agent instances Multiplicity and dynamicity of agent roles Communication, cooperation and negotiation protocols Main classes: Mono-agent Multi-agent cooperative Multi-agent competitive Multi-agent cooperative and competitive With static or dynamic coalitions
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Mathematical Domain of Variables
MAS variables: Parameters of agent percepts, actions and goals Attributes of environment objects Arguments of environment relations, states, events and locations Boolean Discrete Binary Dichotomical Qualitative Nominal Ordinal Interval Quantitative Fractional R Continuous [0,1]
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Mathematical Domain of Variables
Binary: Boolean, ex, Male {True,False} Dichotomic, ex, Sex {Male, Female} Nominal (or categorical) Finite partition of set without order nor measure Relations: only = ou ex, Brazilian, French, British Ordinal (or enumerated): Finite partition of (partially or totally) ordered set without measure Relations: only =, , , > ex, poor, medium, good, excellent Interval: Finite partition of ordered set with measure m defining distance d: X,Y, d(X,Y) = |m(X)-m(Y)| No inherent zero ex, Celsius temperature Fractional (or proportional): Partition with distance and inherent zero Relations: anyone ex, Kelvin temperature Continuous (or real) Infinite set of values
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Other Characteristics
Episodic: Agent experience is divided in separate episodes Results of actions in each episode, independent of previous episodes ex.: image classifier is episodic, chess is not soccer tournament is episodic, soccer game is not Open environment: Partially observable, Non-deterministic, Non-episodic, Continuous Variables, Concurrent Asynchronous, Multi-Agent. ex.: RoboCup, Internet, stock market
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Size and Diversity Size, i.e., number of instances of:
Agent percepts, actions and goals Environment agents, objects, relations, states, events and locations Dramatically affects scalability of agent reasoning execution Diversity, i.e., number of classes of: Agent percepts, actions and goals Environment agents, objects, relations, states, events and locations Dramatically affects scalability of agent knowledge acquisition process
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Agents’ Internal Architectures
Reflex agent (purely reactive) Automata agent (reactive with state) Goal-based agent Planning agent Hybrid, reflex-planning agent Utility-based agent (decision-theoretic) Layered agent Adaptive agent (learning agent) Cognitive agent Deliberative agent
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Reflex Agent Environment Sensors Rules Percepts Action
A(t) = h(P(t)) Effectors
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Remember … Agent Environment Percept Interpretation: I = f(P) P
Reasoning Percept Interpretation: I = f(P) P Sensors Action Choice: A = g(I,O) Goals A Effectors
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So? Environment P Percept Interpretation: I = f(P) Sensors Rules
Effectors Rules Percepts Action A(t) = h(P(t)) A P Goals Percept Interpretation: I = f(P) Action Choice: A = g(I,O)
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Reflex Agent Principle: Wumpus World example Pros: Cons:
Use rules (or functions, procedures) that associate directly percepts to actions ex. IF speed > 60 THEN fine ex. IF front car’s stop light switches on THEN brake Execute first rule which left hand side matches the current percepts Wumpus World example IF visualPerception = glitter THEN action = pick see(glitter) do(pick) (logical representation) Pros: Condition-action rules is a clear, modular, efficient representation Cons: Lack of memory prevents use in partially observable, sequential, or non-episodic environments ex, in the Wumpus World a reflex agent can’t remember which path it has followed, when to go out of the cavern, where exactly are located the dangerous caverns, etc.
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Automata Agent Goals Percept Interpretation Environment Model Update
Rules: percepts(t) model(t) model’(t) Sensors (Past and) Current Enviroment Model Model Update Regras: model(t-1) model(t) model’(t) model’’(t) Goals Action Choice Rules: model’’(t) action(t), action(t) model’’(t) model(t+1) Effectors
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Automata Agent Rules associate actions to percept indirectly through the incremental construction of an environment model (internal state of the agent) Action choice based on: current percepts + previous percepts + previous actions + encapsulated knowledge of initial environment state Overcome reflex agent limitations with partially observable, sequential and non-episodic environments Can integrate past and present perception to build rich representation from partial observations Can distinguish between distinct environment states that are indistinguishable by instantaneous sensor signals Limitations: No explicit representation of the agents’ preferred environment states For agents that must change goals many times to perform well, automata architecture is not scalable (combinatorial explosion of rules)
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Automata Agent Rule Examples
Rules percept(t) model(t) model’(t) IF visualPercept at time T is glitter AND location of agent at time T is (X,Y) THEN location of gold at time T is (X,Y) X,Y,T see(glitter,T) loc(agent,X,Y,T) loc(gold,X,Y,T). Rules model’(t) model’’(t) IF agent is with gold at time T AND location of agent at time T is (X,Y) THEN location of gold at time T is (X,Y) X,Y,T withGold(T) loc(agent,X,Y,T) loc(gold,X,Y,T).
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Automata Agent Rule Examples
Rules model(t) action(t) IF location of agent at time T = (X,Y) AND location of gold at time T = (X,Y) THEN choose action pick at time T X,Y,T loc(agent,X,Y,T) loc(gold,X,Y,T) do(pick,T) Rules action(t) model(t) model(t+1) IF choosen action at time T was pick THEN agent is with gold at time T+1 T done(pick,T) withGold(T+1).
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(Explicit) Goal-Based Agent
Environment Percept Interpretation Rules: percept(t) model(t) model’(t) Sensors (Past and) Current Environment Model Model Update Rules: model(t-1) model(t) model’(t) model’’(t) Goal Update Rules: model’’(t) goals(t-1) goals’(t) Goals Action Choice Rules: model’’(t) goals’(t) action(t) action(t) model’’(t) model(t+1) Effectors
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(Explicit) Goal-Based Agent
Principle: explicit and dynamically alterable goals Pros: More flexible and autonomous than automata agent Adapt its strategy to situation patterns summarized in its goals Limitations: When current goal unreachable as the effect of a single action, unable to plan sequence of actions Does not make long term plans Does not handle multiple, potentially conflicting active goals
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Goal-Based Agent Rule Examples
Rule model(t) goal(t) action(t) IF goal of agent at time T is to return to (1,1) AND agent is in (X,Y) at time T AND orientation of agent is 90o at time T AND (X,Y+1) is safe at time T AND (X,Y+1) has not being visited until time T AND (X-1,Y) is safe at time T AND (X-1,Y) was visited before time T THEN choose action turn left at time T X,Y,T, (N,M,K goal(T,loc(agent,1,1,T+N)) loc(agent,X,Y,T) orientation(agent,90,T) safe(loc(X,Y+1),T) loc(agent,X,Y+1,T-M) safe(loc(X-1,Y),T) loc(agent,X,Y+1,T-K)) do(turn(left),T) Y+1 ok Y v ok A X-1 X
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Goal-Based Agent Rule Examples
Rule model(t) goal(t) action(t) IF goal of agent at time T is to find gold AND agent is in (X,Y) at time T AND orientation of agent is 90o at time T AND (X,Y+1) is safe at time T AND (X,Y+1) has not being visited until time T AND (X-1,Y) is safe at time T AND (X-1,Y) was visited before time T THEN choose action forward at time T X,Y,T, (N,M,K goal(T,withGold(T+N)) loc(agent,X,Y,T) orientation(agent,90,T) safe(loc(X,Y+1),T) loc(agent,X,Y+1,T-M) safe(loc(X-1,Y),T) loc(agent,X,Y+1,T-K)) do(forward,T) Y+1 ok Y v ok A X-1 X
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Goal-Based Agent Rule Examples
Rule model(t) goal(t) goal’(t) //If the agent reached it goal to hold the gold, //then its new goal shall be to go back to (1,1) IF goal of agent at time T-1 was to find gold AND agent is with gold at time T THEN goal of agent at time T+1 is to be in location (1,1) T, (N goal(agent,T-1,withGold(T+N)) withGold(T) M goal(agent,T,loc(agent,1,1,T+M))).
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Planning Agent Environment Percept Interpretation Sensors
Rules: percept(t) model(t) model’(t) (Past and) Current Environment Model Sensors Model Update Rules: model(t-1) model(t) model’(t) model’’(t) Goal Update Rules: model’’(t) goals(t-1) goals’(t) Goals Prediction of Future Environments Rules: model’’(t) model(t+n) model’’(t) action(t) model(t+1) Hypothetical Future Environment Models Action Choice Rules: model(t+n) = result([action1(t),...,actionN(t+n)] model(t+n) goal(t) do(action1(t)) Effectors
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Planning Agent Percept and actions associated very indirectly through:
Past and current environment model Past and current explicit goals Prediction of future environments resulting from different possible action sequences to execute Rule chaining needed to build action sequence from rules capture immediate consequences of a single action Pros: Foresight allows choosing more relevant and safer actions in sequential environments Cons: little point in building elaborated long term plans in, Highly non-deterministic environment (too many possibilities to consider) Largely non-observable environments (not enough knowledge available before acting) Asynchronous concurrent environment (only cheap reasoning can reach a conclusion under time pressure)
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Hybrid Reflex-Planning Agent
Environment Reflex Thread Reflex Rules Percepts Actions Sensors Synchronization Planning Thread Percept Interpretation Current, past and future environment model Current Model Update Future Environments Prediction Effectors Goal Update Goals Action Choice
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Hybrid Reflex-Planning Agent
Pros: Take advantage of all the time and knowledge available to choose best possible action (within the limits of its prior knowledge and percepts) Sophisticated yet robust Cons: Costly to develop Same knowledge encoded in different forms in each component Global behavior coherence harder to guarantee Analysis and debugging hard due to synchronization issues Not that many environments feature large variations in available reasoning time in different perception-reasoning-action cycles
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Layered Agents Many sensors/effectors are too fine-grained to reason about goals using directly the data/commands they provide Such cases require a layered agent that decomposes its reasoning in multiple abstraction layers Each layer represent the percepts, environment model, goals, and actions at a different level of details Abstraction can consist in: Discretizing, approximating, clustering, classifying data from prior layers along temporal, spatial, functional, social dimensions Detail can consist in: Decomposing higher-level actions into lower-level ones along temporal, spatial, functional, social dimensions Decide Abstractly Abstract Detail Perceive in Detail Act in Detail
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Layered Automata Agent
Percept Interpretation Ambiente Sensors Effectors Environment Model Environment Model Update Action Choice and Execution Control Layer2: Layer2: Layer1: Layer0: Layer2: Layer1: Layer0:
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Exemplo de camadas de abstração:
Y
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Abstraction Layer Examples
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Utility-Based Agent Principle:
Goals only express boolean agent preferences among environment states A utility function u allows expressing finer grained agent preferences u can be defined on a variety of domains and ranges: actions, i.e., u: action R (or [0,1]), action sequences, i.e., u: [action1, ..., actionN] R (or [0,1]), environment states, i.e., u: environmentStateModel R (or [0,1]), environment state sequences, i.e., u: [state1, ..., stateN] R (or [0,1]), environment state, action pairs, i.e., u: environmentStateModel x action R (or [0,1]), environment state, action pair sequences, i.e., u: [(action1-state1), ..., (actionN-stateN)] R (or [0,1]), Pros: Allows solving optimization problems aiming to find the best solution Allows trading-off among multiple conflicting goals with distinct probabilities of being reached Cons: Currently available methods to compute (even approximately) argmax(u) do not scale up to large or diverse environments
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Utility-Based Reflex Agent
Environment Sensors Effectors Percept Interpretation: Rules: percept actions Goals Action Choice: Utility Function u:actions R
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Utility-Based Planning Agent
Environment Percept Interpretation Regras: percept(t) model(t) modelo’(t) Sensors Past & Current Environment Model Model Update Regras: model’(t) model’’(t) Future Environment Prediction Regras: model’’(t) ação(t) model(t+1) model’’(t) model(t+1) Hypothesized Future Environments Model Utility Function: u: model(t+n) R Action Choice Effectors
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Adaptive Agent Performance Analysis Component Environment
Sensors Learning Component Performance Analysis Component Acting Component Learn rules or functions: percept(t) action(t) percept(t) model(t) modelo’(t) modelo(t) modelo’(t) modelo(t-1) modelo(t) modelo(t) action(t) action(t) model(t+1) model(t) goal(t) action(t) goal(t) model(t) goal’(t) utility(action) = value utility(model) = value Reflex Automata Goal-Based Planning Utility-Based Hybrid Effectors New Problem Generation Component
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Simulated Environments
Environment simulator: Often themselves internally follow an agent architecture Should be able to simulate a large class of environments that can be specialized by setting many configurable parameters either manually or randomly within a manually selected range ex, configure a generic Wumpus World simulator to generate world instances with a square shaped cavern, a static wumpus and a single gold nugget where the cavern size, pit numbers and locations, wumpus and gold locations are randomly picked Environment simulator processing cycle: Compute percept of each agent in current environment Send these percepts to the corresponding agents Receives the action chosen by each agent Update the environment to reflect the cumulative consequences of all these actions
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Environment Simulator Architecture
Simulation Visualization GUI Rede Environment Update Rules: model(t-1) model(t) action(t) model(t-1) model(t) actions Agent Client 1 Simulated Environment Model percepts Environment Simulation Server ... Agent Client N Percept Generation Rules: model(t) percept(t)
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AI’s Pluridisciplinarity
Economics Sociology Zoology Neurology Psychology (Cognitive) Decision Theory Game Theory Paleontology Linguistics Operations Research Information Theory Mathematics: Logic Probabilities & Statistics Calculus Algebra Computer Science: Theory Distributed Systems Software Engineering Databases Philosophy Artificial Intelligence
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AI Metaphors, Abstractions
AI Roadmap Generic Sub-Fields: Heuristic Search Automated Reasoning & Knowledge Representation Machine Learning & Knowledge Acquisition Pattern Recognition Generic Tasks: Clustering Classification Temporal Projection Diagnosis Monitoring Repair Control Recommendation Configuration Discovery Design Allocation Timetabling Planning Simulation Specific Sub-Fields: Multi-Agent Communication, Cooperation & Negotiation Speech & Natural Language Processing Computer Perception & Vision Robotic Navigation & Manipulation Games Intelligent Tutoring Systems Computational Metaphors: Algorithmic Exploration Logical Derivation Probability Estimation Connectionist Activation Evolutionary Selection Problem Algorithm + P(A|B) AI Metaphors, Abstractions
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Today’s Diversity of AI Applications
Agriculture, Natural Resource Management, and the Environment Architecture & Design Art Artificial Noses Astronomy & Space Exploration Assistive Technologies Banking, Finance & Investing Bioinformatics Business & Manufacturing Drama, Fiction, Poetry, Storytelling & Machine Writing Earth & Atmospheric Sciences Engineering Filtering Fraud Detection & Prevention Hazards & Disasters Information Retrieval & Extraction Knowledge Management Law Law Enforcement & Public Safety Libraries Marketing, Customer Relations & E-Commerce Medicine Military Music Networks - including Maintenance, Security & Intrusion Detection Politics & Foreign Relations Public Health & Welfare Scientific Discovery Social Science Sports Telecommunications Transportation & Shipping Video Games, Toys. Robotic Pets & Entertainment
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AI Pays ! AI Industry Gross Revenue: Companies specialized in AI:
2002: US $11.9 billions Annual growth rate: 12.2% Projection for 2007: $21.2 billions Companies specialized in AI: Corporations developing and using AI: Google, Amazon, IBM, Microsoft, Yahoo, ... Corporations using IA: Wal-Mart, Abbot Labs, US Bancorp, LucasArts, Petrobrás, ... Government agencies using AI: US National Security Agency
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When is a Machine Intelligent? What is Intelligence?
Turing Test ? Who’s smarter? Your medical doctor or your cleaning lady? Your lawyer or your two year old daughter? Kasparov or Ronaldinho? 1997: 2 x 1 2050? What did 40 years of AI research discovered? Common sense intelligence harder than expert intelligence Embodied intelligence harder than purely intellectual, abstract intelligence Kid intelligence harder than adult intelligence Animal intelligence harder than specifically human intelligence (after all we share 99% of our genes with chimpanzees !)
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www.robocup.org New benchmark task for AI
Annual competition associated to conference on AI, Robotics or Multi-Agent Systems
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Tomorrow’s AI Applications
X Blade Runner A.I.
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