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Some people believe that an RPG II program cannot read/update an externally described file. Even though it must be program described in RPG II, it can be a "flat" file (BLDFILE) or externally described (DDS or SQL). Go ahead and externally describe it.
The only drawback to externally defining a S/36 file is that S/36 DFU programs will no longer work. If you're using those, you have to create a native DFU that works off the external definition.
However, if you have a file with multiple record formats, and you don't want to split it into 18 PFs with a multiformat logical to join them, then you'll have a hard time creating a DFU.
For example, we had a S/36 file with a record type code in position 1, and a key in positions 2-13. The rest of the record varied depending on what the code in position 1 was. We tried to externally define it with the following DDS:
midrange.com
A UNIQUE
A R MULTFMT
A RECTYPE 1A
A KEY 12A
A VARDATA 115A
A K KEY
Although this worked fine from RPG II programs, or indeed, any RPG program
that program described the file, it did not work with DFU. The S/36 DFU
refused to even attempt to edit it, saying it was a native file. The
native DFU would always display VARDATA as one big field, and since it
contained packed fields, it often wouldn't display the record at all,
saying that it had illegal characters in it.
Fortunately, this file was only temporary, we ended up completing re-doing the file from the ground up, using modern (well, modern at the time) techniques.
But, I learned my lesson not to create an external definition just so that I could create the file without BLDFILE. :)
Of coruse, when you don't have multiple formats in the file, then it's a no-brainer to externally define it.
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