Re: Early Client Server on the AS/400 -- MIDRANGE-L

Hello Nina,

DDM is available for the PC.  It is described in the manual Using Distributed 
Data Management for the 
IBM Personal Computer, SC21-9643.  I believe the program product is still 
available from IBM although 
I doubt it has been updated in quite some time.

>downsides are pure communication speed.  if your files are large, and you are 
>only
>using a little bit of data, the entire file has to be transmitted.  in some 
>cases,
>this won't work well.

This isn't quite true.  Most of the overhead in DDM is purely due to 
communications line speed.  There 
is some additional overhead when using DDM between AS/400 or S/38 and the DDM 
extensions for those 
platforms are used resulting in extra data being transmitted.  The trade-off is 
reduced processing at 
the source because a more intelligent request can be made of the target system 
but it can result in 
bandwidth limits being reached sooner than expected.

The only instance where an application may suffer additional degradation is 
when duplicate-key files 
are being processed with READE operations.  In this case the source system 
performs a READ-NEXT and 
compares the key value (much like RPG performs with partial-key operations) 
resulting in the 
likelyhood of unnecessary records being returned to the source and discarded.

OPNQRYF can be used to remedy the above situation in most cases because the 
query is sent to the 
target system (using the S/38 and AS/400 DDM extensions) and the target returns 
only the result set -- 
much like SQL and DRDA.  Blocking can also be used for sequential access to 
improve throughput.

Regards,
Simon Coulter.

//----------------------------------------------------------
// FlyByNight Software         AS/400 Technical Specialists
// Phone: +61 3 9419 0175      Mobile: +61 0411 091 400
// Fax:   +61 3 9419 0175      E-mail: shc@flybynight.com.au
// 
// Windoze should not be open at Warp speed.

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Date: Sun, 27 Dec 98 15:32:17 -0600
From: "nina jones" <ddi@datadesigninc.com>
To: MIDRANGE-L@midrange.com
Reply-To: MIDRANGE-L@midrange.com
Subject: Re: Early Client Server on the AS/400

> what do you mean, DDM?   Sounds familiar, but i can remember what this is/was
> exactly.   I'm wondering how the AS/400 database (back in  /94) couldhave been
> accessed remotely from a PC program.    if it could have ...   appreciate your
> help here.

ddm is distributed data management.  it is an easy to use method of sharing data
from one as/400 to another.  you basically say you are using file whatever on
system b instead of your local system.  then, when you process your data it uses
the data just as if you were locally attached.  no programming changes 
necessary.

downsides are pure communication speed.  if your files are large, and you are 
only
using a little bit of data, the entire file has to be transmitted.  in some 
cases,
this won't work well.

i don't know if you can use ddm in an as/400 to p/c environment.

but i seem to recall an article in late 1993 about how to do client server, in
news/400.  i can't remember if it was for os/2 or windows 3/1, but i could check
if it's important.

nj

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