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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 Descriptions Abstractions for Composition Describing Compositions Service Composition as Planning Rules.

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Chapter 15: Agents


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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
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsHighlights of this Chapter
  • Agents Introduced
  • Agent Descriptions
  • Abstractions for Composition
  • Describing Compositions
  • Service Composition as Planning
  • Rules
what is an agent
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsWhat is an Agent?

The term agent in computing covers a wide range of behavior and functionality

  • An agent is an active computational entity
    • With a persistent identity
    • Perceives, reasons about, and initiates activities in its environment
    • Communicates (with other agents) and changes its behavior based on others
  • Business partners => agents
agents and mas for soc
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsAgents and MAS for SOC
  • Why agents for services?
    • Autonomy, heterogeneity, dynamism
  • Unlike objects, agents
    • Are proactive and autonomous
    • Cooperate or compete
    • Model users, themselves, others
    • Dynamically use and reconcile ontologies
modeling agents ai
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsModeling Agents: AI

Traditionally, emphasize mental concepts

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

modeling agents mas
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsModeling Agents: MAS
  • Emphasize interaction
    • Social: about collections of agents
    • Organizational: about teams and groups
    • Legal: about contracts and compliance
    • Ethical: about right and wrong actions
  • Emphasize autonomy and communication
mapping soc to agents
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsMapping SOC to Agents

Agents as components of an open system

  • Autonomy => ability to enter into and enact contracts; compliance
  • Heterogeneity => ontologies
  • Loose coupling => communication
  • Trustworthiness => contracts, ethics, learning, incentives
  • Dynamism => combination of the above
a reactive agent
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsA Reactive Agent

Environment e;

RuleSet r;

while (true) {

state = senseEnvironment(e);

a = chooseAction(state, r);

e.applyAction(a);

}

a rational agent
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsA Rational Agent

Rationality depends on ...

  • A performance measure, e.g., expected utility
  • What the agent has perceived so far
  • What the agent knows ahead of time
  • 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

logic based agents
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsLogic-Based Agents
  • An agent is a knowledge-based system
    • Explicitly represents symbolic model of the world
    • Reasons symbolically via logical deduction
  • Challenges:
    • Maintaining adequate descriptions of the world
    • Representing information about complex real-world entities in symbolic terms
      • Easier in information environments than in general
cognitive architecture for an agent
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsCognitive Architecture for an Agent

For SOC, sensors and effectors are services; communication is via messaging middleware

generic bdi architecture
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

Sensor

input

brf

beliefs

Generate options

desires

filter

intentions

action

Generic BDI Architecture

A BDI architecture addresses how beliefs, desires and intentions are represented, updated, and acted upon

Action

output

architecture of bdi based agent
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsArchitecture of BDI-Based Agent

Execution Cycle: the agent

  • Receives new information
  • Updates beliefs and goals
  • Reasons about actions
  • Intends an action
  • Selects an intended action
  • Activates selected intention
  • Performs an action
  • Updates beliefs, goals, intentions
web ontology language for services owl s
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsWeb Ontology Language for 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
composition as planning
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsComposition as Planning
  • Service composition as planning:
    • Represent current and goal states
    • Represent each service as an action (with inputs, outputs, preconditions, effects)
    • Represent a composed service as a plan that invokes the constituent services constraining the control and data flow to achieve the goal state
rules logical representations
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsRules: Logical Representations
  • Rules are desirable because they are
    • Modular: easy to read and maintain
    • Inspectable: easy to understand
    • Executable: no further translation needed
    • Expressive: (commonly) Turing complete and can capture knowledge that would otherwise not be captured declaratively
      • Compare with relational calculus (classical SQL) or description logics (OWL)
    • Declarative, although imperfectly so
kinds of rules
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsKinds of Rules
  • ECA or Reaction
    • On event if condition then perform action
  • Derivation rules: special case of above
    • Integrity constraints: derive false if error
  • Inference rules
    • If antecedent then consequent
    • Support multiple computational strategies
      • Forward chaining; backward chaining
applying eca rules
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsApplying ECA Rules
  • Capture protocols, policies, and heuristics as rules
    • Examples?
  • Often, combine ECA with inference rules (to check if a condition holds)
  • Modeling challenge
    • What is an event?
    • How to capture composite events by pushing event detection to lower layers
applying inference rules
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsApplying Inference Rules
  • Inference rules capture general requirements well
  • Elaboration tolerance requires defeasibility
    • Write general rules
    • Override them as need to specialize them to account for context
  • Leads to logical nonmonotonicity
    • Easy enough operationally but difficult to characterize mathematically
    • Details get into logic programming with negation
use of variables
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsUse of Variables
  • Need free variables to make the rules generic in how they apply
    • For ECA rules: event and condition
    • For inference rules: antecedent
    • Should generally not have free variables in consequent to ensure “safety”
      • Free variable in action indicates perform action for each binding
      • Free variable in consequent means assert it for each binding
chapter 15 summary
Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael HuhnsChapter 15 Summary
  • Agents are natural fit with open environments
  • Agent abstractions support expressing requirements in a natural manner
  • Agents go beyond objects and procedural programming
  • Self-study Jess