Abstract: A computer system comprising multiple sets of client computers coupled to a database system via a network. Each client computer having installed thereon an application program that comprises client computer specific log-in information. The database system having a log-in component for logging-in the client computers, and being partitioned into multiple relational databases. Each one of the relational databases being assigned to one set of the sets of client computers. Each one of the relational databases storing encrypted data items. Each data item being encrypted with one of the user or user-group specific cryptographic keys. A key identifier of the cryptographic key with which one of the data items is encrypted being stored in the relational database as an attribute of the one of the encrypted data items. The log-in component comprising assignment information indicative of the assignment of the databases to the set of client computers.