ABSTRACT.


A web is a computer designed to meet a specific user requirement through Internet. However. as the user requirements are becoming increasingly complex, a single service falls a short to satisfy complex user requirements independently. Web services composition is an aggregation of multiple services to satisfy complex user requirements with a consistent outcome. To facilitate the composition process and to reach consistent outcome, participating services register with Web services coordination and agreement protocols. However, due to the unreliable nature of these protocols, participating services suffer from errors and failures at a high rate. Current protocol standards offer fault handling but are limited to backward recovery making use of the expensive compensation and rollback strategies. Compensation and rollback are serious issues with the current protocol standards which allow services to run for longer durations. This study provides extensions of the existing Web services coordination and agreement protocol to deal with Web services failures using the forward recovery approach. To serve the purpose, a set of common failure types affecting the execution of participant Web services is identified, and based on that, recovery actions are also proposed. The fault handling extension of the protocol diagnosis and identifies the type of failure at run time and invokes the corresponding recovery solution to recover from the failure in forward recovery fashion. To check the applicability of the extended protocol in real life scenarios, the study is supported by the well-known application example. The implementation and verification of the proposed concepts are accomplished using the model checking and verification tool UPPAAL. To verify the viability and authenticity of proposed extensions, key requirements like the execution of relevant recovery actions in cases of failures and reaching consistent outcome of the completed activity are verified.
Keywords: web services, composition, fault handling, forward recovery, model-
Checking, transaction protocol