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Chapter 15: Agents

Chapter 15: Agents. Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005. Highlights of this Chapter. Agents Introduced Agent Environments Agent Descriptions Abstractions for Composition Describing Compositions

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Chapter 15: Agents

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

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

  3. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  4. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  5. Dimensions of MAS: Agent Adaptivity (the ability of an agent to learn): Autonomy: Interactions: Sociability (awareness): Fixed Teachable Autodidactic Controlled Interdependent Independent Simple Complex Autistic Committing Collaborative Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  6. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  7. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  8. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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

  10. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  11. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  12. Agent Environments • Communication Infrastructure • Shared memory (blackboard) • Connected or Connectionless (email) • 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) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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

  14. 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? Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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

  16. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  17. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  18. Cognitive Architecture for an Agent Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  19. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  20. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  21. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  22. Sensor input brf beliefs Generate options desires filter intentions action Generic BDI Architecture Action output Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  23. Architecture of BDI-Based Agent Execution Cycle: • New information arrives that updates beliefs and goals • Actions are triggered by new beliefs or goals • A triggered action is intended • An intended action is selected • That intention is activated • An action is performed • New beliefs or goals are stored • Intentions are updated Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  24. 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  25. OWL-S Service Ontology Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  26. OWL-S Compared to UDDI Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  27. OWL-S Service Model Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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

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

  30. Composition as Planning Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

  31. Rules Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

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

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