1. 1 Exception Handling in Goal- Oriented Multi-Agent Systems İbrahim Çakırlar, Erdem Eser Ekinci and Oğuz Dikenelli Ege University Computer Engineering Department İzmir, Turkiye

2. 2 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 2

3. 3 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. 3

4. 4 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. 4

5. 5 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 5

6. 6 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 6

7. 7 Exception Handling Mechanism for Goal-oriented Multi-agent Systems 7

8. 8 Goal-oriented multi-agent system executable entities : system goal, agent goal, plan. In MASs, execution flow designed with the terms of cooperation and standalone. 8

9. 9 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 9

10. 10 Exception Handling Mechanism for Goal-oriented Multi-agent Systems We categorized exception levels due to hierarchy of executable entities. Exception Level EntityStandaloneCooperative MAS LevelSystem Goal Agent LevelAgent Goal Plan LevelPlan 10

11. 11 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 11

12. 12 Exception Handling Mechanism for Goal-oriented Multi-agent Systems 12

13. 13 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 13

14. 14 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 14

15. 15 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 15

16. 16 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 16

17. 17 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. 17

18. 18 Our Implementation - Decision making Cycle 18 All exceptions are occur in this step. Plan Level is handled in this step. But for other levels the cycle goes on.

19. 19 Our Implementation – Execution Sample Goal Model Plan Model Dynamically added when an exception occurs 19

20. 20 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 20

21. 21 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.

22. 22 Case Study : Electronic Barter Application Goal Model of exchangeBarterProducts System Goal

23. 23 Exceptional Execution Flow Plan Level Exception Handling Definition HTN Plan for evaluateBarterPropo sal agent goal Exception Handling Task for UnavaibleDatabase Exception Plan Level Exception Definition For HTN Tasks 23

24. 24 Agent Level Exception Handling Customer 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

25. 25 Agent Level Exception Handling Goal Model Exceptional agent goal definition 25

26. 26 Multi-agent Level Exception Handling inverseOf definition between system goals inverseOf 26

27. 27 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 27

28. 28 Other Exception Handling Approaches We categorize other exception handling approaches in two main category. Organizational View Agent View 28

29. 29 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 29

30. 30 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. 30

31. 31 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. 31

32. 32 Comparison of Exception Handling Approaches 32 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.

33. 33 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 33

34. 34 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. 34

35. 35 Thanks, any questions? 35