I. Introduction
As a new concept of software application model, Software as a Service (SaaS) provides a unique platform to tenant, which helps them directly access Software Applications via the intemet[1], [2]. In this model, the Service Provider host the application instances and manage them, while the tenant who want to use the SaaS applications just need to rent them instead of buying licenses. For small and medium enterprises, SaaS model is an efficient way to use the enterprise applications [3]. They don't need to pay extra fees for constructing and maintaining applications' basis. To meet the different requirements of tenant, SaaS applications should be configurable and multi-tenant aware [4].