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
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
Work Flow of the Replication Manager
Reliable Web Service Paradigm
9
Design DiversityParallel 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.

1 2 3 4 5 6 7 8
Spatial replication 0 0 0 0 1 1 1 1
Reboot 0 0 1 1 0 0 1 1
Retry 0 1 0 1 0 1 0 1
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
Communication time Computation time 14314 (101)
Total requests and frequency 10000 requests (1 per min)
Load 78.5
Timeout period of retry 1 min
Timeout for Web service in RM 1s (Web service specific)
Polling frequency 10 requests per min
Number of replicas 5
Max number of retries 5
Round-robin rate 1 s
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

• 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

Web Service Composition
22
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

Web Service Composition
23
Web Service Composition
24
Web Service Composition

1. Output
2. Operation in WSDL
3. Find the output information in CP1 (Web service
   component)
4. 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
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
Reliability Model
Modeling
34
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
QA