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Exception Handling in Goal-Oriented Multi-Agent Systems

İbrahim Çakırlar, Erdem Eser Ekinci and Oğuz DikenelliEge University Computer Engineering Departmentİzmir, Turkiye

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Overview

•Introduction•Exception Handling Mechanism for Goal

Oriented MASs•Abstact Exception Handling Architecture

for MASs•Our Implementation•Case Study : Electronic Barter Application•Other Exception Handling Approaches•Conclusion

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Introduction

•Exception handling is based on the exception concept that is defined in software systems such as an error occurred during execution flow of a program.

•Traditional technologies like Object Oriented Programming(OOP) try to satisfy reliability and robustness properties via exception handling.

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Introduction

•Classical exception handling techniques can not be applied to MASs for the reason of some properties:▫cooperative, ▫autonomy, ▫open,▫distributed.

•In this research we design a specialized exception handling approach for MASs.

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• Introduction

• Exception Handling Mechanism for Goal Oriented MASs

• Abstact Exception Handling Architecture for MASs

• Our Implementation

• Other Exception Handling Approaches

• Case Study : Electronic Barter Application

• Conclusion

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

•In many cases and researches exception handling is considered as a later step of development process.

•Lamsweerde and Letier* also claim using goals to model exception handlers at the requirement analysis phase of goal-oriented MAS development.

*Axel van Lamsweerde and Emmanuel Letier. Handling obstacles in goal-oriented requirements engineering. Software Engineering, 26(10) :9781005, 2000

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

•Goal-oriented multi-agent system executable entities : system goal, agent goal, plan.

•In MASs, execution flow designed with the terms of cooperation and standalone.

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

•We propose a layered exception hierarchy like Platon*.

•Exception levels ▫Multi-Agent Level▫Agent Level▫Plan Level

* Eric Platon, Nicolas Sabouret, and Shinichi Honiden. An architecture for exception management in multi-agent systems. International Journal on Agent-Oriented Software Engineering, 2008

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

•We categorized exception levels due to hierarchy of executable entities.

Exception Level

Entity Standalone Cooperative

MAS Level System Goal

Agent Level Agent Goal

Plan Level Plan

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

•In our principle, conveniently with the simplicity principle of Goodenough*, claim that each exception should be handled with the executable entities that are same level with the exception occurred in.

•If it can not be handled in the same level, it hampers the execution flow of one upper level. So,it should be handled in the upper level.

* John B. Goodenough. Exception handling design issues. SIGPLAN Not., 10(7):41 -45, 1975

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Exception Handling Mechanism for Goal-oriented Multi-agent Systems

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• Introduction

• Exception Handling Mechanism for Goal Oriented MASs

• Abstact Exception Handling Architecture for MASs

• Our Implementation

• Case Study : Electronic Barter Application

• Other Exception Handling Approaches

• Conclusion

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Abstract Exception Handling Architecture of MASs

•Three phase of agent cyclic execution model; perception, reasoning and action.

•As other operations exception handling spreads over the same execution model.

•Perception phase Reasoning Phase Action Phase

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Abstract Exception Handling Architecture of MASs

•Perception phase: Perception of exceptional/ unexpected situation.

•Reasoning phase: Decide exception cause, occurance level and handling level

•Action phase : Apply decided exception handling policy

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• Introduction

• Exception Handling Mechanism for Goal Oriented MASs

• Abstact Exception Handling Architecture for MASs

• Our Implementation

• Case Study : Electronic Barter Application

• Other Exception Handling Approaches

• Conclusion

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Our Implementation

•Our abstract exception handling architecture is implemented in SEAGENT Multi-Agent Development Framework.

•The primitive properties of SEAGENT are semantic web enability, goal orientation and HTN based plan execution.

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Our Implementation - Decision making Cycle

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All exceptions are occur in this step.

Plan Level is handled in this step. But for other levels the cycle goes on.

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Our Implementation – Execution SampleGoal

Model

PlanModel

Dynamically added when an exception occurs

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• Introduction

• Exception Handling Mechanism for Goal Oriented MASs

• Abstact Exception Handling Architecture for MASs

• Our Implementation

• Case Study : Electronic Barter Application

• Other Exception Handling Approaches

• Conclusion

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Case Study : Electronic Barter Application

Customer Agent1

Customer Agent2

Barter Management

Agent Cargo Agent

Barter Proposals

matching

Notifiy Customer Agent for evaluating the Barter Requests

Sends evaluation result

Notify for organizing Product Transport

Transport Information

Transport information is notified.

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Case Study : Electronic Barter Application Goal Model of

exchangeBarterProducts System Goal

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Exceptional Execution Flow

Plan Level Exception Handling Definition

HTN Plan for evaluateBarterProposal agent goal

Exception Handling Task

for UnavaibleDataba

seException

Plan Level Exception Definition

For HTN Tasks

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Agent Level Exception HandlingCustomer

Agent1

Customer Agent2

Barter Management

Agent

Barter Proposals

matching

Notifiy Customer Agent for evaluating the Barter Requests

When an exception occurs the regular execution flow is changed.

Customer agent cancels the proposal

The proposal of crashed agent is cancelled

Participant agents are notified

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Agent Level Exception Handling Goal Model

Exceptional agent goal definition

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Multi-agent Level Exception Handling

inverseOf definition between

system goals

inverseOf

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• Introduction

• Exception Handling Mechanism for Goal Oriented MASs

• Abstact Exception Handling Architecture for MASs

• Our Implementation

• Case Study : Electronic Barter Application

• Other Exception Handling Approaches

• Conclusion

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Other Exception Handling Approaches•We categorize other exception handling

approaches in two main category.

•Organizational View

•Agent View

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Other Exception Handling Approaches•Organizational View: These approaches

bring some organizational entities to MAS and these entities monitor agents by listening their internal events and messages to detect exceptional situations.

▫Centralized

▫Decentralized

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Other Exception Handling Approaches• Centralized organizational view define an

exception handling entity in the architecture of MAS for handling exceptions.

▫Tripathi and Miller's guardian agent▫Klein and Dellarocas's Exception Handling

Service(EHS).

• Decentralized organizational view spread responsibility of handling exceptions through more than one organizational entity.

▫Haegg's sentinel agents.

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Other Exception Handling Approaches

• Agent View: These approches listen messages and events of the agent, but they propose a mechanism to handle the exceptions inside the agent.

▫SaGE framework.

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Comparison of Exception Handling Approaches

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• Organizational views’ definitions are weak, they need so much information and resource (agents/services) for handling exceptions.

• Decentralized views need an agent for each agent.

• Organizational views do not consider agent internal knowledge.

• Organizational views do not support agent autonomy.

• Agent views focus on agent internal exceptions, do not consider organizational exceptions.

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• Introduction

• Exception Handling Mechanism for Goal Oriented MASs

• Abstact Exception Handling Architecture for MASs

• Our Implementation

• Case Study : Electronic Barter Application

• Other Exception Handling Approaches

• Conclusion

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Conclusion

•We propose an exception handling approach for goal-oriented MASs.

•Our approach is classified in agent view but MAS Level Exception make it applicable in organizational view.

•And we propose life cycle that supports autonomy of agents.

•Its obeserved with the case study that our approach support the robustness and reliability of MASs.

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Thanks, any questions?

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