On Repairing Web Services Workflows

When a composite web service-i.e., a composition of individual web services-is executed and fails, it is desirable to reuse as much as possible the results that have been obtained thus far. For example, a travel agent, after receiving an order to arrange for a trip from LA to NY from a customer, would typically identify the flights and the hotels, obtain the confirmation from the customer, and place the reservations using the credit card information provided by the user; if something is wrong (e.g., at the last step, the credit card information was wrong), the travel agent would prefer to place the reservations using another means (e.g., a different card) instead of starting from the beginning.This paper introduces an approach for dealing with service failures in the context of workflow execution. The paper defines the notion of a web service composition (WSC) problem and the notion of a solution workflow for a WSC problem. The paper describes two approaches to repair a partially executed workflow, with the goal of effectively reusing parts of the workflow that have been successfully executed. The usefulness of these approaches are demonstrated in an implementation using Answer Set Programming (ASP) in the well-known shopping domain.