Developing Aerospace Applications with a Reliable Web Services Paradigm

1. Developing Aerospace Applications with a Reliable Web Services Paradigm Pat. P. W. Chan and Michael R. Lyu Department of Computer Science and Engineering The Chinese University of Hong Kong IEEE 2008 Aerospace Conference

2. Outline • Introduction • Problem Statement • Methodologies for Web Service Reliability • New Reliable Web Service Paradigm • Optimal Parameters • Experimental Results • Web Service Composition Algorithm • Experimental Results • Discussion • Modeling of the Paradigm • Conclusion and Future Work

3. Introduction • Web services provide an efficient and convenient way for service provisioning, exchanging and aggregating, which facilitate a resourceful platform for the aerospace industry. • Complex synthesis of various aerospace technologies and sciences can be provided in the form of Web services. • In aerospace area, reliability is an ultimately important issue. • Existing Web service model needs to be extended to assure reliability. • We propose a paradigm with a roadmap to dependable Web services. Introduction

4. Problem Statement • Fault-tolerant techniques • Replication • Diversity • Replication is one of the efficient ways for providing reliable systems by time or space redundancy. • Increase the availability of distributed systems • Key components are re-executed or replicated • Protect against hardware malfunctions or transient system failures • Another potential technique is design diversity • Employ independently designed software systems or services with different programming teams, • Defend against permanent software design faults. • We focus on the analysis of the replication techniques when applied to Web services. • A generic Web service system with spatial as well as temporal replication is proposed and investigated. Introduction

5. Replication Manager Web Service RR Algorithm / Voting Web Service Web Service IIS Application IIS IIS Database WatchDog Application Application Invoke Web service Database Database Client Port Application UDDI Update the WSDL Register Database Registry Keep check the availability of all Web services. If a Web service failed, update the list of availability of Web services WSDL Look up Get WSDL The Proposed Paradigm Reliable Web Service Paradigm

6. Different Approaches • Replication • Round-robin scheduling algorithm • Design Diversity • N-version programming • Recovery block Reliable Web Service Paradigm

7. Replication: Round-robin Reliable Web Service Paradigm

8. Gets reply Does not get reply Update the Web service availability list RM sends message to the Web Service All Services failed System Failure Map the new address to the WSDL after RR Work Flow of the Replication Manager Reliable Web Service Paradigm

9. Design Diversity:Parallel N-Version Programming Reliable Web Service Paradigm

10. Design Diversity: Recovery Block Reliable Web Service Paradigm

11. Experiments Variations • A series of experiments are designed and performed for evaluating the reliability of the Web service. Reliable Web Service Paradigm

12. System Testing • Best Route Finding. • Provide traveling suggestions for users. • Starting point and destination. • The system needs to provide the best route and the price for the users. Reliable Web Service Paradigm

13. System Architecture Reliable Web Service Paradigm

14. Experimental Setup Reliable Web Service Paradigm

15. Experimental Results (1) Web Service Composition

16. Experimental Results (2) Web Service Composition

17. Experimental Results (3) Web Service Composition

18. Experimental Results (4) Web Service Composition

19. Summary of the Proposed Paradigm • Temporal replication (reboot or retry) improves the reliability. • Spatial replication further improves the reliability of Web services. • N-version programming approach is the most effective choice. Reliable Web Service Paradigm

20. Web Service Composition Algorithm • N-version programming • Reliability improvement • Effective • Composition • WSDL – Web Services Description Language • WSCI – Web Services Choreography Interface • Verification • BPEL – Business Process Execution Language • Petri-Net Web Service Composition

21. WSDL <?xmlversion="1.0" encoding="UTF-8"?> … <portTypename=“BRF"> <operationname=“shortestpath"> <inputmessage="tns:startpointDestination"/> <outputmessage="tns:pathArray"/> </operation> <operationname=“addCheckpoint"> <inputmessage="tns:pathArray"/> <outputmessage="tns:addAcknowledgement"/> </operation> … </operation> </portType> </definitions> Web Service Composition

22. WSCI <correlationname=“pathCorrelation”property=“tns:pathID”></correlation> <interfacename=“busAgent”> <processinstantiation="message"> <sequence> <actionname="ReceiveStartpointDest“role="tns:busAgent“ operation="tns:BRF/shortestpath"> </action> <actionname="Receivecheckpoint“role=" tns:busAgent“ operation="tns:BRF/addCheckpoint"> <correlatecorrelation=“tns: pathCorrelation”/> <callprocess=“tns:SearchPath”/> </action> </sequence> </process> … Web Service Composition

23. Web Service Composition

24. CP4 CP7 CP10 Else, till the root of WSCI Web Service Composition • Output • Operation in WSDL • Find the output information in CP1 (Web service component) • If Input of the operation == required input CP1 • Else • search in the WSCI of CP1 to find action == operation • Get the pervious action involved • Search in WSDL to find operation == action • If Input of the operation == required input Web Service Composition

25. Search Agent Bus Agent Train Agent Bus: KMB Train: MTR Starting P1 Starting P2 Web Service Composed Tree Web Service Composition

26. Web Service Composition

27. Petri-Net– Basic Activities Web Service Composition

28. Petri-Net– Structure Activities Web Service Composition

29. Composed Petri-Net Web Service Composition

30. Web Service Composition

31. Web Service Composition

32. Summary of the Web Service Composition Algorithm • The composition algorithm is proposed with the use of WSDL and WSCL • The BPEL of the composed Web services are generated • Petri-Net is employed to avoid deadlock • Acceptance tests are set for checking the correctness • Experiments are performed • Efficient • Accurate • Deadlock-free Web Service Composition

33. λN (1-c1)μ* (1-c1)μ* S F μ*c2 (1-c1)μ* μ*c2 S-1 S-2 S-n λ* λ* λ* (a) (1-c1)μ1 μ1c2 P1 (1-c2)μ1 λ1 S-j S-j-1 F μ2c2 (1-c2)μ2 λ2 (1-c1)μ2 P2 (b) Reliability Model Modeling

34. ID Description Value λn Network failure rate 0.02 λ* Web service failure rate 0.025 λ1 Resource problem rate 0.142 λ2 Entry point failure rate 0.150 μ* Web service repair rate 0.286 μ1 Resource problem repair rate 0.979 μ2 Entry point failure repair rate 0.979 C1 Probability that the RM response on time 0.9 C2 Probability that the server reboot successfully 0.9 Reliability Model Modeling

35. Outcome (SHARPE) Modeling

36. Conclusions • Surveyed replication and design diversity techniques for reliable services and the state-of-the-art Web service composition algorithm. • Proposed a hybrid approach to improving the reliability of Web services. • Proposed a Web service composition algorithm and verified by Petri-Net. • Carried out a series of experiments to evaluate the availability and reliability of the proposed Web service system. • Employ Markov chain to model the system and analyze its reliability and performance. Conclusion and Future Work

37. Future Work • Improve the current fault-tolerant techniques • Current approach can deal with hardware and software failures. • How about software fault detectors? • N-version programming • Different providers provide different solutions. • There is a problem in failover or switch between the Web Services. • Application • Different requirements • Realize in the Internet. Conclusion and Future Work

38. Q&A