Data security is a topic of high interest in many application fields. Especially in the medical field, sensitive patient data must be secured from unauthorized access. In the GS-BAMOD research project sensitive patient data is processed in a Grid infrastructure. In such an environment, security is still a greater concern. The existing security modules do not satisfy the project''s demands. This work first identifies the database security requirements of the GS-BAMOD project. These requirements suggest a new security mechanism that enables a Fine-Grained access control on a Role- Basis. Building on that, a general model for implementing such mechanisms is described. A major feature of this model is that it is applicable to existing databases without interfering with its structure. Two implementations of this model are presented, that support secured reading access to databases. The working principles and implementation details of both implementations are described. Later, a comparison of the two approaches is given. The security related advantages and disadvantages of both implementations are described. At the end, future extension possibilities are pointed out.