Re: Subfile processing with duplicate keys

-----Original Message-----
From: Vernon Hamberg <hambergv@goldengate.net>
To: MIDRANGE-L@midrange.com <MIDRANGE-L@midrange.com>
>
>Another 'geezer' topic :-)
>
>At 08:24 PM 5/13/1998 -0400, you wrote:
>>What is a multiformat logical file?  I don't understand why the RRN isn't
>>unique and therefore suitable...?  (I don't question you, I just don't
>>understand it.  If its what I think it is, this must just one of many
>>problems you have to overcome.)
>
>-snip-
>
>Multis combine multiple physical files that contain similar keys (I think)
>under one logical file. They are read in the key order. RRNs are
>meaningless, since you're looking at many physicals, hence you can have the
>same RRN for different records.
>
>It's an AS/400 (IBM?) only technique, originating somewhere before true
>logicals or something. I don't really know the history, just that they are
>associated with S36 in my thinking.

Wheeze, gasp, hack...

All right, you young 'uns, listen up:

Multi-format logicals were implemented on the S/38 to simplify porting of
S/3 (and therefore S/32, S/34, and S/36) applications to the /38.  Those
systems all provided for files which had several different record formats in
them, since the only defining points of their files were 1) record length
and 2) key position and length.  One can't externally define a physical file
on the /38 or /400 with multiple record formats in a meaningful manner, so
the designers came up with this thing called a multi-format logical, plus
another piece called a record format selector program, to enable the
"logical" merging of several physicals together to simulate the function of
the original S/3 or whatever file.  RPG II batch programs could be compiled
with the /38's RPG III compiler and still work, even though the files were
now externally defined so that new programs could use the definitions, as
well as utilities like Query/38 and DFU for the /38 (available at the Little
IBM Shop of Horrors, of course).

Note that this was considered a very important capability because the /38
was originally sold as the upgrade path for S/3 shops that had outgrown
their hardware.  It's kind of hard today to think of a /38 Model 7 as an
upgrade from anything (except maybe a Model 4), but that's the situation.

In reply to the original questioner,  the simplest solution is to change the
program to use the underlying physicals and forget the multi-format logical.
The things are historical curiosities that cause more problems than they
solve in modern, interactive programs.  This is just my humble opinion, of
course.

Dave Shaw, General Nutrition, Greenville, SC (just down the road from BMW -
Bubba Makes Wheels :)
The opinions expressed may not be my employer's unless I'm sufficiently
persuasive...



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