How Does Web Service API Evolution Affect Clients?

Like traditional local APIs, web service APIs (web APIs for short) evolve, bringing new and improved functionality as well as incompatibilities. Client programs have to be modified according to these changes in order to use the new APIs. Unlike client programs of a local API, which could continue to use the old API, clients of a web API often do not have the option not to upgrade, since the old version of the API may not be provided as a service anymore. Therefore, migrating clients of web APIs is a more critical task. Research has been done in the evolution of local APIs and different approaches have been proposed to support the migration of client applications. However, in practice, we seldom observe that web API providers release automated tools or services to assist the migration of client applications. In this paper, we report an empirical study on web API evolution to address this issue. We analyzed the evolution of five popular web APIs, in total 256 hanged API elements, and carefully compared our results with existing empirical study on API evolution. Our findings are threefold: 1) We summarize the API changes into 16 change patterns, which provide grounded supports for future research, 2) We identify 6 completely new challenges in migrating web API clients, which do not exist in the migration of local API clients, 3) We also identify several unique characteristics in web API evolution.