Context-oriented programming for customizable SaaS applications

Software-as-a-Service (SaaS) applications are multi-tenant software applications that are delivered as highly congurable web services to individual customers, which are called tenants in this context. For reasons of complexity management and to lower maintenance cost, SaaS providers maintain and deploy a single version of the application code for all tenants. As a result, however, custom-made extensions for individual tenants cannot be eciently integrated and managed. In this paper we show that by using a context-oriented programming model, cross-tier tenant-specic software variations can be easily integrated into the single-version application code base. Moreover, the selection of which variations to execute can be congured on a per tenant basis. Concretely, we provide a technical case study based on Google App Engine (GAE), a cloud platform for building multitenant web applications. We contribute by showing: (a) how ContextJ, a context-oriented programming (COP) language, can be used with GAE, (b) the increase in exibility and customizability of tenant-specic software variations using ContextJ as compared to Google's dependency injec tion framework Guice, and (c) that the performance of using ContextJ is comparable to Guice. Based on these observa- tions, we come to the conclusion that COP can be helpful for providing software variations in SaaS.