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Chapter 15: Agents Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005.

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Presentation on theme: "Chapter 15: Agents Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005."— Presentation transcript:

1 Chapter 15: Agents Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005

2 Chapter 152Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Highlights of this Chapter Agents Introduced Agent Environments Agent Descriptions Abstractions for Composition Describing Compositions Composition as Planning Rules

3 Chapter 153Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agents and MAS for SOC Why the interest in agents for Web services? Need for autonomy, heterogeneity, dynamism Unlike conventional services, agents Know about themselves, their users, and their competitors Use and reconcile ontologies Are proactive and communicative Are autonomous about their commitments Can be cooperative

4 Chapter 154Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns What is an Agent? The term agent in computing covers a wide range of behavior and functionality. In general, an agent is an active computational entity with a persistent identity that can perceive, reason about, and initiate activities in its environment that can communicate (with other agents) and change their behavior based on others These features make agents a worthwhile metaphor in computing

5 Chapter 155Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Dimensions of MAS: Agent Adaptivity (the ability of an agent to learn): Autonomy: Interactions: Sociability (awareness): FixedTeachableAutodidactic ControlledIndependent SimpleComplex Interdependent AutisticCollaborativeCommitting

6 Chapter 156Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Abstractions/1 The traditional abstractions are from AI and are mentalistic beliefs: agent’s representation of the world knowledge: (usually) true beliefs desires: preferred states of the world goals: consistent desires intentions: goals adopted for action

7 Chapter 157Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Abstractions/2 The agent-specific abstractions are inherently interactional social: about collections of agents organizational: about teams and groups ethical: about right and wrong actions legal: about contracts and compliance

8 Chapter 158Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Abstractions/3 Agents, when properly understood lead naturally to multiagent systems provide a means to capture the fundamental abstractions that apply in all major applications and which are otherwise ignored by system builders

9 Chapter 159Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agents versus AI

10 Chapter 1510Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns How to Apply the Abstractions Consider how the components of a large and dynamic software system in a practical situation Dynamism => autonomy Openness and compliance => ability to enter into and obey contracts Trustworthiness => ethical behavior

11 Chapter 1511Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Why Do These Abstractions Matter? Because of modern applications that demand going beyond traditional metaphors and models Virtual enterprises: manufacturing supply chains, autonomous logistics, Electronic commerce: utility management Communityware: social user interfaces Problem-solving by teams

12 Chapter 1512Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Environments Communication Infrastructure Shared memory (blackboard) Connected or Connectionless ( ) Point-to-Point, Multicast, or Broadcast Directory Service Communication Protocol FIPA ACL HTTP and HTML RMI, OLE, CORBA, DCOM, etc. Interaction Protocol, i.e, conversations such as contracting Mediation Services Security Services (timestamps/authentication/currency) Remittance Services Operations Support (archiving/billing/redundancy/restoration/accounting)

13 Chapter 1513Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns A Reactive Agent in an Environment Environment e; RuleSet r; while (true) { state = senseEnvironment(e); a = chooseAction(state, r); e.applyAction(a); }

14 Chapter 1514Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Characteristics of Agent Environments Observability: can all aspects relative to actions be sensed? Determinism: is next state completely determined by current state + agent’s action? History Freedom: does action choice depend on previous episodes or just current episode? Dynamism: can environment change while agent is deliberating? Continuity: do the agent actions, environment state variables, and time points have a continuous range of values? Multiagent: is the agent aware of others that can affect the environment?

15 Chapter 1515Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Architectures If the environment is viewed as a set of states, S={s 1,s 2 ….} and the actions of an agent can be viewed as the set A = {a 1,a 2 ….} then, an agent can be abstractly viewed as an action S*  A, which maps a sequence of environment states to an action The behavior of an environment can be modeled as a function Env: S x A  Subset{S} An agent’s interaction with its environment can be represented as a history h, where h = (a 0, s 0 )  ( a 1,s 1 )  ( a 2,s 2 )  …(a u, s u )  (a u+1,s u+1 ) …

16 Chapter 1516Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Architectures Logic-Based Reactive Belief-Desire-Intention (BDI) Layered Architecture

17 Chapter 1517Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Logic Based Agents Decision making is realized through logical deduction View the agents as particular type of knowledge based system Contains an explicitly represented symbolic model of the world Takes decisions via symbolic reasoning Problems: Translating the real world into an accurate adequate symbolic description, in real-time How to represent information symbolically about complex real-world entities

18 Chapter 1518Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns A Rational Agent Rationality depends on... The performance measure for success What the agent has perceived so far What the agent knows about the environment The actions the agent can perform An ideal rational agent: for each possible percept sequence, it acts to maximize its expected utility, on the basis of its knowledge and the evidence from the percept sequence

19 Chapter 1519Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Cognitive Architecture for an Agent

20 Chapter 1520Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Reactive Architecture Does not rely on symbol manipulation, e.g., Rodney Brooks’ subsumption architecture Intelligent behavior can be generated without explicit representations proposed by symbolic AI Intelligent behavior can be generated without explicit abstract reasoning Intelligence is an emergent property of certain complex systems

21 Chapter 1521Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Subsumption Architecture A hierarchy of task-accomplishing behaviors Each behavior is a rather simple rule-like structure Each behavior competes with others to exercise control over the agent Lower layers present more primitive kinds of behavior In terms of computation, the resulting systems are extremely simple

22 Chapter 1522Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns BDI Deciding on what goals to achieve and how to achieve them Beliefs – the information an agent has about its surroundings Desires – the things that agent would like to see achieved Intentions – things that an agent is committed to doing A BDI architecture addresses how beliefs, desires and intentions are represented, updated and processed

23 Chapter 1523Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Action output brf Generate options filter action Sensor input beliefs desire s intentions Generic BDI Architecture

24 Chapter 1524Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Architecture of BDI-Based Agent Execution Cycle: 1. New information arrives that updates beliefs and goals 2. Actions are triggered by new beliefs or goals 3. A triggered action is intended 4. An intended action is selected 5. That intention is activated 6. An action is performed 7. New beliefs or goals are stored 8. Intentions are updated

25 Chapter 1525Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Layered Architecture Decompose the system into different layers to deal with different types of behaviors Typically at least two layers – to deal with reactive and proactive behaviors Broadly, two types of control flow within layered architectures Horizontal layering Vertical layering

26 Chapter 1526Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Layer n … Layer 1 Layer 2 Layer 3 Layer n … Layer 1 Layer 2 Layer 3 Layer n … Layer 1 Layer 2 Layer 3 Horizontal LayeringVertical Layering (one pass control) Vertical Layering (two pass control) Perceptual Input Action Output Perceptual Input Action Output Perceptual Input Layered Architecture

27 Chapter 1527Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Web Ontology Language – Services (OWL-S) An OWL-S service description provides Declarative ads for properties and capabilities, used for discovery Declarative APIs, used for execution A declarative description of services -- based on their inputs, outputs, preconditions, and effects -- used for composition and interoperation

28 Chapter 1528Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns OWL-S Service Ontology

29 Chapter 1529Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns OWL-S Compared to UDDI

30 Chapter 1530Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns OWL-S Service Model

31 Chapter 1531Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns OWL-S Example: Processing Book Orders

32 Chapter 1532Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns OWL-S IOPE’s for Bookstore Example

33 Chapter 1533Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Composition as Planning

34 Chapter 1534Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Rules

35 Chapter 1535Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Chapter 15 Summary


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