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:
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.
We have developed EPIC database software version 1.0 which support
Ingres databases. Recently we have re-designed database system
(EPIC database version 2.0) and we choose MySQL
database as our primary database management system. Please refer
to EPIC Database Management Using MySQL
presentation for more information.