The FATMEN catalogue is maintained in a ZEBRA RZ (FORTRAN direct access) file.
These files, one per experiment, are updated only by dedicated servers, again one per experiment. Updates are sent in FZ ASCII exchange format to these servers, which then read them in and apply them to the RZ database.
The RZ structure, being based on the Unix file system with the addition of cycles or versions as in the VMS operating system, provides base for the FATMEN file catalogue. In an RZ database, a directory contains data identified by a number of keys. In the FATMEN file catalogue, these keys include the filename (i.e. that part of the generic name that follows the last slash, the pathname maps directly to the RZ pathname), the location code, medium type and copy level (original, copy, copy of a copy etc.).