Web Service Transactions

1
Web Service Transactions

• Group Members
• Nirmit Desai
  Ajay Dudani
• Sandeep Kachru
  Kunal Shah
• March 6, 2003

2
Outline of the talk

• Introduction
• Transactions for Web Services
• Transactional Attitudes Overview
• Example of a system with Transactional Attitudes
• Questions Comments

3
Introduction

• A transaction is a mechanism to insure all the
  participants in an application achieve a mutually
  agreed outcome
• Web Services provide a distributed computing
  environment
• Support for transactions are fundamental to
  reliable distributed computing environments

4
Transactions for Web Services

• Web Services are message oriented middleware, as
  compared to object oriented middleware like CORBA
• Existing solutions of Web Service transactions
  are limited
• Restricted programming flexibility
• Transactions are supported in application rather
  than in middleware
• Increased application complexity
• No QoS guarantees
• There is no way to specify interdependence
  between different web service

5
Transactional Attitudes Overview

• Implement transactions as web service
• Total possible attitudes for transaction models
  supported is limited
• Have predefined set of possible transaction
  attitudes
• Provider Transaction Attitudes
• Pending Commit
• Group Pending Commit
• Commit compensate
• Client Transaction Attitudes
• Implicit Transaction Attitudes
• Explicit Transaction Attitudes

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Transactional Attitudes Overview (2)

• In order to have support for transactions, one
  needs
• Operations that are provided by provider for
  transaction support
• Information on how these operations map to
  transaction state machine
• Information of transaction outcome and its
  interpretation
• We use extensions to WSDL to incorporate some of
  the above requirements
• Extensions to WSDL help up identify the
  operations provided for transaction support and
  transaction attitude supported by the provider
• Lets look at some examples to understand this

7
Outline of the talk

• Introduction
• Transactions for Web Services
• Transactional Attitudes Overview
• Example of a system with Transactional Attitudes
• Provider Transaction Attitudes
• Client Transaction Attitudes
• Extensions to WSDL
• Usage Scenario

8
Provider Transaction AttitudesPending Commit

• In pending commit PTA, there exists a single
  forward operation that can be held in pending
  state until the following event that determines
  if the transaction is success or failure
• Example Airline systems

Book Ticket
Initial State
Block Ticket
Cancel Ticket
9
Provider Transaction AttitudesGroup Pending
Commit

• In group pending commit PTA, there exists a
  multiple forward operation that can be held in
  pending state until the following event that
  determines if the transaction is success or
  failure
• Example Taxi booking

Book taxi reservation
Reserve taxi from A to B
Reserve taxi from B to C
Reserve taxi from C to D
Cancel taxi reservation
10
Provider Transaction AttitudesCommit Compensate

• In commit compensate PTA, there is no
  transaction model supported by the provider.
  The only way to rollback the previous
  transaction is to cancel it.
• Example Hotel Reservation

Reserve Room 1
Initial State
Commit Operation
Cancel Room Reservation
Initial State
Commit Compensate Operation
11
Client Transaction AttitudesImplicit Client
Attitude

• In implicit CTA, i.e. in the absence of
  transaction web service framework, the client
  implicitly describes output of transactional
  operations on the provider and manages the
  rollback conditions on its own
• Example
• Send request to block 2 flights
• Send request to book one hotel room
• Send request to book taxi
• If both flights are booked and also hotel is
  booked, then commit all operations
• If either of airline or hotel booking fails then
  rollback all operations

12
Client Transaction AttitudesExplicit Client
Attitude

• In explicit CTA, i.e. in the presence of
  transaction web service framework, the client
  informs the transaction web service of the
  transactions it wants to perform and defines the
  success condition of the transactions. All the
  rest is handled by the transaction web service.
• Example Usage Scenario follows

13
Extensions to WSDL

• Extensions to WSDL are used to specify the
  transaction attitude supported by the provider
  and to mark an operation as prepare operation,
  commit operation, rollback operation
• Examples
• lttx transactionPending-Commitgt
• lttxforwardOperationgt blockFlight
  lt/txforwardOperationgt
• lttxcommitOperationgt reserveFlight
  lt/txcommitOperationgt
• lttxabortOperationgt cancelFlight
  lt/txabortOperationgt
• lttxcompensateOperationgt cancelRoom
  lt/txcompensateOperationgt

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Usage Scenario
15
Usage Scenario (2)
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References

• Transactional Attitudes Reliable Composition of
  Autonomous Web Services by Thomas Mikalsen,
  Stefan Tai, Isabelle Rouvellou
• Conditional Messaging Extending Reliable
  Messaging with Application Conditions by Stefan
  Tai, Thomas Mikalsen, Isabelle Rouvellou, Stanley
  M. Sutton Jr.
• Question Comments