TRUSTWORTHY COORDINATION OF WEB SERVICES ATOMIC TRANSACTION
To protect the core services described in the WS-AT (Web Services Atomic Transactions) specification namely Activation Service, Registration Service ,the Completion Service and the Coordinator Service against Byzantine Fault.
Driven by the need for business collaboration and integration, more and more applications are being deployed over the Internet using Web Services technology. Many such applications involve distributed transaction processing. To provide interoperability among transactional Web Services, the Web Services Atomic Transactions (WSAT) specification was developed by a consortium of companies (led by Microsoft and IBM) and was recently adopted by OASIS as one of the Web Services standards.
ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â The Coordinator Services offers sets of services to the initiator and the participants of a transaction name Activation,Registration,Completion and Coordinator service’s. The Activation Service creates a coordinator object and a transaction context for each new transaction. The Registration ServiceÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â creates a context for participant into the transaction. The Completion service initiates the distributed commit of the transaction at the request of the Initiator. ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â The Coordinator service coordinates the Participants to ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â commit or abort the transaction atomically
The BFT (Byzantine Fault Tolerance) framework uses a lightweight ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â protocol instead of running an instance of Byzantine ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â agreement for registration of each Participant. The protocol ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â utilizes, at each Participant, the collection of registration ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â acknowledgments from a quorum of Coordinator replicas, ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â and a round of message exchange at the start of the two- ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â phase commit protocol. These mechanisms ensure that, if a ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â non-faulty Participant has registered with the Coordinator, ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â the Participant is included in the two-phase commit.
Moreover, if the number of Participants is large, these ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â mechanisms reduce the overhead dramatically.
In the existing system WS-AT services rendered Byzantine fault tolerant by replicating the WS-ATÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â services and ensuring Byzantine Agreement (BA) of theÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â replicas on every operation using an existing Byzantine Fault Tolerance (BFT) algorithmÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â such as Practical Byzantine Fault Tolerance (PBFT) such approach is approach is not practical, because executing ByzantineÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â agreement on every operation is prohibitively expensive
In our BFT ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â framework for trustworthy coordination of Web Services ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â Atomic Transactions that exploits the semantics of the WS- AT interactions to achieve better performance than a ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â general-purpose BFT algorithm that is theoreticallyÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â applied. ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â We recognize that not every operation in WS-AT requires ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â Byzantine agreement among the Coordinator replicas and, ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â thus, that the total number of Byzantine agreements needed ÃƒÆ’Ã¢â‚¬Å¡Ãƒâ€šÃ‚Â in a typical transaction can be sharply reduced.