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Building Reliable Web Services: Methodology, Composition, Modeling and Experiment

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Protect against hardware malfunctions or transient system faults ... Find the output information in CP1 (Web service component) ... – PowerPoint PPT presentation

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Title: Building Reliable Web Services: Methodology, Composition, Modeling and Experiment


1
Building Reliable Web Services
Methodology,Composition, Modeling and Experiment
  • Pat. P. W. Chan
  • Department of Computer
  • Science and Engineering
  • The Chinese University of
  • Hong Kong

23 October 2007
2
Outline
  • Introduction to Web Services
  • Problem Statement
  • Methodologies for Web Service Reliability
  • New Reliable Web Service Paradigm
  • Web Service Composition Algorithm
  • Experimental Results and Discussion
  • Conclusion

3
Introduction
  • Service-oriented computing is becoming a reality.
  • The problems of service dependability, security
    and timeliness are becoming critical.
  • We propose experimental settings and offer a
    roadmap to dependable Web services.

4
Problem Statement
  • Fault-tolerant techniques
  • Replication
  • Diversity
  • Replication is one of the efficient ways for
    providing reliable systems by time or space
    redundancy.
  • Increasing the availability of distributed
    systems
  • Key components are re-executed or replicated
  • Protect against hardware malfunctions or
    transient system faults
  • Another efficient 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.

5
Proposed Paradigm
6
Round Robin
7
Parallel N-Version Programming
8
Recovery Block
9
Experiments
  • A series of experiments are designed and
    performed for evaluating the reliability of the
    Web service,

10
Testing system
  • 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.

11
System Architecture
12
Experimental Setup
  • Examine the computation to communication ratio
  • Examine the request frequency to limit the load
    of the server to 75
  • Fix the following parameters
  • Computation to communication ratio (e.g 101)
  • Request frequency

13
Experimental Setup
14
Experiment Parameters
  • Fault mode
  • Temporary (fault probability 0.01)
  • Permanent (fault probability 0.001)
  • Experiment time 5 days (7200 requests)
  • Measure
  • Number of failures
  • Average response time (ms)
  • Failure definition
  • 5 retries are allowed. If there is still no
    correct result from the Web service after 5
    retries, it is considered as a failure.

15
Experimental Result with Round-robin (failures /
response time in ms)
16
Experimental Result with N-Version (failures /
response time in ms)
17
Experimental Result with Recovery Block (failures
/ response time in ms)
18
Web Service Composition Algorithm
  • N-version programming
  • Reliable
  • Efficient
  • Composition
  • WSDL
  • WSCI
  • Verification
  • BPEL
  • Petri-Net

19
WSDL
  • lt?xml version"1.0" encoding"UTF-8"?gt
  • ltportType nameBRF"gt
  • ltoperation nameshortestpath"gt
  • ltinput message"tnsstartpointDestination"/gt
  • ltoutput message"tnspathArray"/gt
  • lt/operationgt
  • ltoperation nameaddCheckpoint"gt
  • ltinput message"tnspathArray"/gt
  • ltoutput message"tnsaddAcknowledgement"/gt
  • lt/operationgt
  • lt/operationgt
  • lt/portTypegt
  • lt/definitionsgt

20
WSCI
  • ltcorrelation namepathCorrelation
    propertytnspathIDgtlt/correlationgt
  • ltinterface namebusAgentgt
  • ltprocess instantiation"message"gt
  • ltsequencegt
  • ltaction name"ReceiveStartpointDest
    role"tnsbusAgent
  • operation"tnsBRF/shortestpath"gt
  • lt/actiongt
  • ltaction name"Receivecheckpoint role"
    tnsbusAgent
  • operation"tnsBRF/addCheckpoint"gt
  • ltcorrelate correlationtns
    pathCorrelation/gt
  • ltcall processtnsSearchPath/gt
  • lt/actiongt
  • lt/sequencegt
  • lt/processgt

21
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22
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

23
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24
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25
Petri-Net Basic Activities
26
Petri-Net Structure Activities
27
Composed Petri-Net
28
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29
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30
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31
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32
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33
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34
Petri-Net (Four identical replicas)
35
Petri-Net (N-version Web service with voting)
36
Petri-Net (Recovery Block)
37
Reliability Model
38
Reliability Model
39
Outcome (SHARPE)
40
Conclusion
  • Surveyed replication and design diversity
    techniques for reliable services.
  • Proposed a hybrid approach to improving the
    availability 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.

41
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