A method and a system access data of a database in a MES system by a client application where the database access is required to satisfy a set of custom data protection rules depending on a set of user credentials. The method includes providing, at developing time a secure access layer for enabling the client application to access data to/from the database in a protected manner taking into account the set of custom data protection rules; and at runtime or engineering time by the client application, requesting, through a given authenticated user, data access to/from the database by sending to the secure access layer a given data access descriptor and the given user credentials of the given authenticated user. By the secure access layer, the received data access descriptor is processed to generate a given SQL statement for data access.