Re: Logical Files vs. Physical Keys

[boothm@xxxxxxxxxxxxxxxxx]

It used to be that if you created a  primary file with a key then you 
could not change the key.  A lot of shops made the decision to never key 
the physical as they'd been burned too often with the "this field will 
never change" promise, which is a great deal like "the field will never be 
any larger than this, we guarantee it" promise.


_______________________
Booth Martin
boothm@earth.goddard.edu
http://www.spy.net/~booth
_______________________




"Nelson C. Smith" <ncsmith@gate.net>
Sent by: owner-midrange-l@midrange.com
03/25/2000 01:13 AM
Please respond to MIDRANGE-L

 
        To:     <MIDRANGE-L@midrange.com>
        cc: 
        Subject:        Re: Logical Files vs. Physical Keys


If you add referential constraints to the unkeyed physical, the system 
will
put a primary key on it anyway.

----- Original Message -----
From: "Bale, Dan" <DBale@TFSA.Textron.com>
To: <MIDRANGE-L@midrange.com>
Sent: Thursday, March 23, 2000 10:28 AM
Subject: RE: Logical Files vs. Physical Keys


> No, the reason why many shops kept the physical unkeyed was because,
> apparently, in the early days (S/38 and early AS/400?), if the access 
path
> on a physical file became corrupted, there was a good chance that you
could
> not recover the data from the physical file.  From what I've heard over
the
> years, this has become less of a risk.  Perhaps even no risk, but I'll
defer
> to others more knowledgeable than me.
>
> Otherwise, I am unaware of any reason why you should not key the 
physical
> file.  Someone else already mentioned this, and I concur, that the
physical
> file should be defined with a unique key.
>
> My .02
>
> - Dan Bale
>
> -----Original Message-----
> From: Kmcmann@marzetti.com [mailto:Kmcmann@marzetti.com]
> Sent: Thursday, March 23, 2000 8:35 AM
> To: MIDRANGE-L@midrange.com
> Subject: RE: Logical Files vs. Physical Keys
>
>
> I don't know if this might have been your reason, but way back on the
S/36,
> we did the same thing, just because changes could be made to alternative
> index keys, but not to parent file keys.
>
> > -----Original Message-----
> > From: Bob Entwistle [SMTP:bentwist@famousfootwear.com]
> > Sent: Wednesday, March 22, 2000 6:16 PM
> > To: MIDRANGE-L@midrange.com
> > Subject: Logical Files vs. Physical Keys
> >
> >
> >
> > When we started out on the AS400 11 years ago, a decision was made to
> > always use
> > logical files and never use physical keys (index) on all of our files.
At
> > this
> > point, this is being reevaluated and no one seems to remember why
physical
> > keys
> > were seen as a bad thing.
> >
> > Anyone able to give a short synopsis of the tradeoffs between the two?
> > Any
> > downsides to using physical keys or indexes?
> >
> > Bob
> >
> >
> >
> >
> >
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