As stated above, there can be multiple entries in the FATMEN catalogue for a given generic name. These entries correspond to different copies of a given dataset. In a typical case, the master copy may be on a cartridge at CERN, another copy at RAL, with a disk copy on the workstation cluster at the pit.
For a given generic name, only one entry can exist with the same host name and dataset name, if the dataset resides on disk or with the same volume serial number (VSN), visual identifier (VID) and file sequence number (FSEQ) for tape resident datasets.