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EPIC Database Management

Local PMEL EPIC data management and database communications on Unix

PMEL EPIC data residing on UNIX workstation disks is managed with an INGRES database on an INGRES licensed server machine. The INGRES database contains metadata from the data files. The data itself resides in individual disk files and is not entered into INGRES. INGRES contains metadata and pointers to the individual data files. The data files can be located at any machine, but loading the INGRES database requires that the data disks be mounted by the INGRES licensed machine so that metadata from the data file can be loaded directly into the INGRES database. Click here for details about PMEL's EPIC INGRES data base.

The information loaded into INGRES tables includes the path and name of the data file, geographic range, depth range, time range, cruise ID, cast number, etc. This information can be retrieved by a user via the EPIC selection programs on any networked UNIX machines. The metadata in the INGRES tables can be accessed by one the following methods:

• Using command line interactive selection program
• Using World Wide Web browser
• Using Motif based X-window application

All of the data selection procedures utilize Remote Procedure Calls (RPCs) to perform the task. The RPC model contains two parts of processes-- one is the caller's (user from any machine) process, the other is a server's (the machine providing network service) process. The server's process on the server machine is dormant awaiting the arrival of a call message from a client machine. When one arrives, the server process extracts the the procedure's parameters, computes the results, sends a reply message and the awaits the next call message. The following figure demonstrates how the Romote Procedure Call model is used in EPIC/INGRES database data selection program.

The EPIC/INGRES database data selection program (the client procedures) send the selection query parameters and search constaints with RPC calls to the INGRES server machine. When the server machine receives the message, its service daemon will invoke the service procedure to search the INGRES database, select the data file, and then send the result back to the client procedure. When client procedure receives the message from the server, the results of the procedures are exracted to generate the pointer file (list of data files meeting the users selection criteria) on the local system.