Chapter 15 Agents ServiceOriented Computing Semantics Processes Agents

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

Highlights of this Chapter n n n Chapter 15 Agents Introduced Agent Descriptions Abstractions for Composition Describing Compositions Service Composition as Planning Rules Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 2

What is an Agent? The term agent in computing covers a wide range of behavior and functionality n An agent is an active computational entity n With a persistent identity n Perceives, reasons about, and initiates activities in its environment n Communicates (with other agents) and changes its behavior based on others n Business partners map to agents Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 3

Agents and MAS for SOC n Unlike objects, agents n n n In addition, agents may n n n Chapter 15 Are proactive and autonomous Support loose coupling Cooperate or compete Model users, themselves, and others Dynamically use and reconcile ontologies Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 4

Modeling Agents: AI n Emphasize mental concepts n n n Chapter 15 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 5

Modeling Agents: MAS n Emphasize interaction n n Chapter 15 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 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 6

Mapping SOC to Agents apply well in an open system n n n Chapter 15 Autonomy ability to enter into and enact contracts; compliance Heterogeneity ontologies Loose coupling communication Trustworthiness contracts, ethics, learning, incentives Dynamism combination of the above Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 7

A Reactive Agent Environment e; Rule. Set r; while (true) { state = sense. Environment(e); a = choose. Action(state, r); e. apply. Action(a); } Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 8

Rationality A performance measure, e. g. , expected utility n An agent’s prior knowledge and perceptions n The available actions An ideal rational agent: for each possible n percept sequence, it acts to maximize its expected utility, on the basis of its knowledge and the evidence from the percept sequence Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 9

Logic-Based Agents n An agent is a knowledge-based system n n n Represents a symbolic model of the world Reasons symbolically via logical deduction Challenges: n Representing information symbolically n n Chapter 15 Easier in information environments than in general Maintaining adequate model of the world Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 10

Cognitive Architecture for an Agent For SOC, sensors and effectors map to services; communication is via messaging middleware Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 11

Generic BDI Architecture Sensor input Addresses how beliefs, desires and intentions are represented, updated, and acted upon brf beliefs Generate options desires filter intentions action Action output Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 12

Architecture of BDI-Based Agent Execution Cycle: the agent 1. Receive new information 2. Update beliefs and goals 3. Reason about actions 4. Intend an action 5. Select an intended action 6. Activate selected intention 7. Perform an action 8. Update beliefs, goals, intentions Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 13

Web Ontology Language for Services (OWL-S) An OWL-S service description provides n Declarative ads for properties and capabilities n n Declarative APIs n n Used for execution A declarative description via inputs, outputs, preconditions, effects (IOPE) n Chapter 15 Used for discovery Used for composition and interoperation Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 14

OWL-S Service Ontology Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 15

OWL-S Compared to UDDI Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 16

OWL-S Service Model Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 17

OWL-S Example: Processing Book Orders Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 18

OWL-S IOPEs for Bookstore Example Chapter 15 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 19

Composition as Planning n n Represent current and goal states Represent each service as an action n n Chapter 15 Based on its IOPE Represent a composed service as a plan that invokes the constituent services constraining the control and data flow to achieve the goal state Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 20

Rules: Logical Representations n Rules are desirable because they are n Modular: easy to read and maintain n Inspectable: easy to understand n Executable: no further translation needed n Expressive: (commonly) Turing complete and can capture knowledge that would otherwise not be captured declaratively n n Chapter 15 Compare with relational calculus (classical SQL) or description logics (OWL) Declarative, although imperfectly so Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 21

Kinds of Rules n ECA or Reaction n n Derivation rules: special case of above n n On event if condition then perform action Integrity constraints: derive false if error Inference rules n n If antecedent then consequent Support multiple computational strategies n Chapter 15 Forward chaining; backward chaining Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 22

Applying ECA Rules n Capture protocols, policies, and heuristics as ECA rules n n n Often, combine ECA with inference rules (to check if a condition holds) Modeling challenge n n Chapter 15 Examples? What is an event? How to capture composite events by pushing event detection to lower layers Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 23

Applying Inference Rules n n Capture general requirements Elaboration tolerance requires defeasibility n n n Leads to logical nonmonotonicity n n Chapter 15 Formulate general rules Override rules to specialize them as needed Easy enough operationally but difficult to characterize mathematically Details get into logic programming with negation Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 24

Free and Bound Variables n General rules involve free variables n For ECA rules: in event and condition n n For inference rules: in antecedent n n Chapter 15 Free variable in action indicates perform action for each binding Free variable in consequent means assert it for each binding Therefore, to ensure safety, use only bound variables in action or consequent Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 25

Chapter 15 Summary n n n Chapter 15 Agents are natural fit with open environments Agent abstractions support expressing requirements in a natural manner Agents go beyond objects and procedural programming Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns 26