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OSTs differ from Tab-Delimited Files (TDF) in that data is
stored in its original form in an OST. Binary data is stored
in binary form and character data is stored in character form.
TDFs store all data in character form. TDFs use column and
record delimiters; OSTs do not. TDFs provide some compression
of textual data with trailing whitespace. This is not currently
available with an OST, but is slated as a near future enhancement.
- In complex queries, it may be advantageous to accumulate
results to an intermediate table. Several queries may need
to append to the same intermediate table so, once complete,
a final SELECT statement can be issued against the intermediate
table.
- In large data warehouses, it may be advantageous to preserve
certain aggregations in a temporary rollup table. Subsequent
queries may read this temporary rollup table, thus avoiding
the re-aggregation of the original data.
- It may be desirable to have multiple processes access
the same SELECT...INTO table. While SELECT...INTO produces
a table that can be recorded in the environment file and
then accessed by multiple processes, this is not a realistic
option in many applications. OST's can serve the same purpose
and may be accessed immediately by multiple processes.
OST's are created using the EXPORT command.
Create an OST by exporting data with the OST option. The
resulting file will contain a ".ost" suffix on NT,
UNIX and VMS platforms, and an "OT" suffix on MPE/XL.
OST's can then be accessed by attaching them real-time to
the process using the Omnidex Query Language ATTACH command.
Once attached, they can be accessed as a normal file. The
OST can be detached using the Omnidex Query Language DETACH
command.
An OST is known only to the current process, but may be attached
to multiple processes and multiple environments. An attached
OST remains a part of the environment for the life of the
current process or until a DETACH command is executed.
OST's can be also declared in the environment file as a permanent
file. Declare the table TYPE as OST and use the PHYSICAL clause
to identify the file, minus the suffix.
At this time it is not possible to install indexes on OST's.
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