Interoperability among independently evolving Web services

The increasing popularity of XML Web services motivates us to examine if it is feasible to substitute one vendor service for another when using a Web-based application, assuming that these services are "derived from" a common base. If such substitution were possible, end users could use the same application with a variety of back-end vendor services, and the vendors themselves could compete on price, quality, availability, etc. Interoperability with substituted services is non-trivial, however, and four types of incompatibilities may arise during such interoperation - structural, value, encoding and semantic. We address these incompatibilities three-fold: (1) static and dynamic analysis tools to infer whether an application is compatible with a substituted service, (2) semiautomatically generated middleware components called cross-stubs that actually resolve incompatibilities and enable interoperation with substituted services, and (3) a lightweight mechanism called multi-option, types to enable applications to be written from the ground up in an interoperation-friendly manner. Using real applications and services as examples, we both demonstrate and evaluate our tools and techniques for enabling interoperation with substituted services.