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13 Database commands Database commands are divided into two groups metadata management commands biometric data management commands Metadata management commands include CreateUser, AddUserTo Subset, Remove UserFromSubset, as well as commands for biographic data management - SetBiographicData, GetBiographicData, Delete BiographicData and ListBiographicData. It is important to note that metadata also consists of users' biographical information. It is clear that in addition to storing multimodal biometric data in the database, it is also required to save information about users. New user in the database can be created using the CreateUser command. There is also an option to define user subsets in the database (.e. users from Europe, America, Asia.). Users' belonging to a subset can be defined by issuing AddUser To Subset command. On the other hand, it is also possible to remove the user from the specified subset by using the RemoveUserFromSubset command, Setting biographical information for the user can be done by calling the SetBiographicData command, Deleting biographical data from the database is done with Delete Biographic Data command. Proposed protocol also provides mechanism for viewing biographical data. Certain biographical data can be extracted from the database by issuing the GetBiographicData command. Also, ListBiographicData enables system user to list all biographical data for a targeted user Figure 3: Database commands class diagram Biometric data management includes similar commands as in biographical data management group. Those commands are SetBiometricSample, GetBiometric Sample, Delete Biometric Sample and ListBiometricData. Using SetBiometric Sample a biometric sample for a certain user is recorded in the database. If you need to retrieve biometric sample from the database, it can be done by issuing the GetBiometricSample command To delete saved biometric sample of an user, DeleteBiometricSample command can be used. Also, it is possible to extract all biometric samples of desired user by using the ListBiometricData command. Multimodal commands Multimodal commands are those that are used to utilize the functionalities provided by a multimodal biometric system. FuseScores and FuseScoresList commands are members of this category. Using the FuseScores command, matching scores obtained by executing the verification process are fused. By issuing the FuseScoresList command, fusion of matching scores obtained by executing identification process is done. When using both of these commands it is required to define fusion algorithm that is desired to be applied in fusion process. The difference between verification scores fusion and identification scores fusion is that verification process returns only one matching score per modality, while identification process returns a list of matching scores. Thus, the result of FuseScores command is the score calculated by using selected fusion algorithm. On the other hand, issuing FuseScoresList command results with a list of scores calculated by applying selected fusion algorithm on identification matching scores list. MultimodalProtocol Message FuseScores FuseScorestit Figure 4: Multimodal commands class diagram