Path: utzoo!attcan!uunet!mcsun!ukc!axion!vision!chris
From: chris@vision.UUCP (Chris Davies)
Newsgroups: comp.databases
Subject: Updating remote database locally
Message-ID: <1110@vision.UUCP>
Date: 11 Jun 90 13:50:27 GMT
Reply-To: chris@vision.UUCP (Chris Davies)
Organization: VisionWare Ltd., Leeds, UK
Lines: 42

We have the situation where users would like to be able to access some Unix
database and do the following:

	1.  retrieve a set of records
	2.  change them *locally* (on a PC/Workstation)
	3.  update the remote database

As I see it, record-level locking would help here, so assume this exists
and can be used to prevent several users updating the same records at the
same time.

So far, no problem.  Now extend point 2 to include the addition of new
records (no user will add the same (new) record).

The problem(s) occur in the following scenario:

	1.  user creates new record XYZ locally
	2.  remote database is updated to include record XYZ
	3.  user changes local copy of record XYZ
	4.  remote database is updated

How can I ensure that the remote database's copy of XYZ is updated, rather than
a new copy of this record being inserted?

My initial thought is that I could repeat the SELECT (which defines the set of
records to be downloaded to the PC/Workstation) between (2) and (3), but I
would like to avoid this if possible, since this would be fairly expensive
(in terms of data transfer to the PC/Workstation).

If I could arrange that each record (new or otherwise) had a unique identifier,
this might help.

Comments please!?  If you email me, I'll summarise to the net later.

Many thanks,
		Chris
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