The logical structure of the FATMEN user/server interaction
is shown in figure 
on page .
The FATMEN catalogue is accessed in read-only mode, using FORTRAN
direct-access or C I/O. The catalogue itself may be local or remote -
this is completely transparent to the user. All that is required is that
a symbol (VAX/VMS systems) or environmental variable (Unix systems) is
defined, giving the location of the catalogue.
In this way, remote catalogues may be accessed using NFS [10],
DFS [11], in VAXcluster systems,
using the SHIFT [12]
remote file I/O software, or using other remote file access techniques,
as they become available.
Updates to the catalogue are made by writing update files in a subdirectory of the directory containing the catalogue itself. These updates are processed by a dedicated server, which applies the updates to the catalogue and sends them to all other servers that are defined. In addition, the updates are saved as journal files in a special directory. The updates may be transmitted using a variety of network protocols. The default is via TCP/IP, but the exact method is chosen using a configuration file.
When building the servers, one may also activate code that causes the updates to be applied both to the normal catalogue which is retained in a ZEBRA RZ file, and also in a relational database, such as ORACLE. This second database is not normally seen by users (unless they explicitly invoke SQL commands) and is maintained principally for backup purposes.
Figure: The logical structure of the FATMEN user/server interaction
Figure: The FATMEN user/server interaction on VM/CMS systems
Figure: Interacting with the FATMEN database via the ZEBRA server
