Re: user record updates, locking, and logical vs physical record access

"COBOL400-L" <cobol400-l-bounces@xxxxxxxxxxxx> wrote on 08/06/2016
01:00:02 PM:

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Date: 08/06/2016 01:00 PM
Subject: COBOL400-L Digest, Vol 14, Issue 23
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Today's Topics:

1. Re: user record updates, locking, and logical vs physical
record access (CRPence)

----- Message from CRPence <crpbottle@xxxxxxxxx> on Fri, 05 Aug 2016
16:34:35 -0500 -----

To:

COBOL400-L@xxxxxxxxxxxx

Subject:

Re: [COBOL400-L] user record updates, locking, and logical vs
physical record access

On 05-Aug-2016 14:58 -0500, Stone, Joel wrote:

<<SNIP>> what if the file being updated is a logical view with only
10% of the total fields in the record. In that case, one would have
to work with the PF just in case one of the non-visible fields was
changed by another user? <<SNIP>>

The application can only effect change to the fields visible through
that LF record format. Thus by comparison of the previous record-image
to the current record-image, necessarily inclusive only of the fields
included in the format, the application knows whether the data that is
capable of being changed has not been changed, since, by someone else,
so the update is safe; i.e. same as for the physical record, but the
posited logical record has less data available both to compare and as
able to be changed.

That said, I can imagine that a triggered _before event_ logic for a
secondary changer, could potentially introduce a conflict for the
physical data of a change made by another updater to that same row, but
the business rules implemented by a trigger probably would not generally

be something for which such conflicts should arise; i.e. probably such a

problematic trigger had implemented something that would not properly
qualify as a business-rule, for which the operation must always occur
irrespective the means to effect that I\O request, including that of
logical vs physical.

--
Regards, Chuck

I have one other word of caution when dealing with logical views having a
limited set of fields from the physical. Be very careful if you use them
in a program that adds records. The fields which are not included in the
logical will get the database defaults. Without review of what those
default values would be, you can end up with some corrupt or erroneous
data--and sometimes that won't show up for quite some time.

Michael Quigley
Computer Services
The Way International
www.TheWay.org