The FORTRAN callable interface provides all of the functionality of the command line interface and more. As the user has direct access to all of the information in the file catalogue, subject to normal security restrictions, he is able to perform much more sophisticated operations on the various fields of the file catalogue. Basically, the command line interface provides access to information which is essential to safe retrieval of the data, whereas the FORTRAN callable interface allows the user to manipulate the data according to user-defined fields, to override values in the database and so on.