From: Thorbjørn Ravn Andersen

Have I understood this correctly? You describe that using ISAM you can
navigate the index file very easily - does that lock you in advance to
using THIS particular index file and no others?

I'm sorry, Thorbjørn, but I don't even understand this question. With ISAM,
the index is separate from the data file; you can have as many indexes as
you need. In i5/OS, the physical file is the data file, the logical file is
the index.

Your program can use as many or as few logical files as it needs. The only
thing you can't do in this situation is read records in an order for which
you do not already have a logical file (and even then you can use OPNQRYF,
embedded SQL or even create a logical view on the fly).

The major advantage of SQL in a long term setting is that is is
disconnected from the actual database tables and indexes, and it does
what is necessary to get the job done.

This is simply not true. In order to have an SQL application perform with
any sort of acceptable performance, you MUST predefine indexes and/or views.
It's really no different from creating the appropriate logical views in an
ISAM environment.

The ONLY time you would not use a pre-defined VIEW or INDEX is when it is a
truly ad hoc query, which would correspond to the OPNQRYF statement above.

The idea that SQL allows you to not care about the layout of the database is
really not supported in the real world.


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