The logical structure of the FATMEN user/server interaction is shown in figure [more info] on page [more info]. 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 [bib-NFS], DFS [bib-DFS], in VAXcluster systems, using the SHIFT [bib-SHIFT] 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
+---------------------------------------------------------------------------+ | | | | | | | | | | | | | | | | | | | | | | | | | | | NO FILE: fatfig0.eps | | | | | | | | | | | | | | | | | | | | | | | | | | | +---------------------------------------------------------------------------+ [FATFIG0]
Figure: The FATMEN user/server interaction on VM/CMS systems
+--------------------+ | | | | |NO FILE: fatfig1.eps| | | | | | | | | +--------------------+ [FATFIG1]
Figure: Interacting with the FATMEN database via the ZEBRA server
+--------------------+ | | | | |NO FILE: fatfig2.eps| | | | | | | | | +--------------------+ [FATFIG2]