In the previous years, Cloud computing has attracted a large variety of applications which are completely deployed on resources of Cloud providers. As data management is an essential part of these applications, Cloud providers have to deal with many different requirements for data management, depending on the characteristics and guarantees these applications are supposed to have. The objective of a Cloud provider is to support these diverse requirements in a cost-effective way with a basic set of customizable modules and protocols that can be (dynamically) combined. Thus, for the application providers, it is essential that the needs of their applications are provided in a cost-optimized manner. In our work, we are developing PolarDBMS, a flexible and dynamically adaptable system for managing data in the Cloud. PolarDBMS derives policies from application and service objectives. Based on these policies, it automatically deploys the most efficient and cost-optimized set of modules and protocols and monitor their compliance. If necessary, the PolarDBMS concept allows to dynamically exchange modules and/or their customization.