RPG - conversion vs re-write

[peteh@xxxxxxxxxxxxxxxx (Pete Hall)]

In message <3.0.16.19970908122813.1b075414@mailhost.ideasoft.com>, From 
"Carlos Penengo" <Carlos@ideasoft.com>, the following was written:
> I'm looking for opinions on past experiences with migrating an RPG II 
> app from a S/36 to AS/400 RPG IV. Does a simple conversion do the job 
> or does it have to be re-written to take full advantage of the AS/400 
> native environment?

Carlos,

I used to do conversions for a living, and I'd have to say that it
depends on what you mean by taking "full advantage". OCL can be
converted to CL, but it will be UGGLY and inefficient. If it is done
properly however, it will exactly duplicate the function of the original
OCL, and perform at least as well as it ever did on the S36. You'll have
very minimal retraining issues to deal with. However, in order to get
clean, efficient native code, you must rewrite. The implication of this
is that design changes will be required in order to take advantage of
the services and capabilities of the AS/400. 

RPG and Cobol code will not benefit a great deal performance-wise from a
rewrite, but if you are doing design changes to clean up the CL, some
rewriting will be necessary. How much will be determined by the nature
of the changes and the coding style of the programs. If you wish to take
full advantage of externally described files, activation groups,
procedures, bound program calls, etc, you will need to rewrite much of
the code. This will be significant for ease of future maintenance, but
not necessarily for performance.

The way to go depends on your goals. How long will this code remain in
production? Is it archaic now or will it be so in the near future? If
so, go for quick and dirty. How much of it is critical for the business?
Is maximum performance a necessity? If so, is that for only certain
parts of the system? There's no compelling need to do the whole system
the same way. You could rewrite critical parts and batch convert the
rest, tweaking as the need arises. Actually, this last is what I've
recommended most often, since it usually gives you the best return on
investment. Even a "quick and dirty" job can be a major undertaking for
some systems.

hth
Pete


--
 - Pete Hall peteh@earth.inwave.com
http://www.inwave.com/~peteh/

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