syncing two pcs

[Mike or Penny Novack]

Flynn, Oweson O wrote:

>Hi,
>
>I have found a stunning app for M$ Windows, that allows you to
>synchronise both ways - it shows you which one is newer, can show you
>only differences - well worth a look at - it will allow you to keep your
>copy of your data file synchronised.
>
>I use it to sync the Outlook PST mail files between my work machine and
>my home PC - I copy the files onto a USB drive, and use it to update the
>older copy (which ever one that is).
>
>The App is called 'Beyond Compare 2' - go look at
>http://www.scootersoftware.com/   
>
>Hope this helps!
>  
>
Misconception? Misunderstanding/disagreement about the term "newer".

In the third example I was NOT meaning to imply that a program could not 
be written to do exactly what you just described. Use "time stamp" to 
mediate the decision about which version/changes to use. Thus the 
program would always give a definite result (the result of the 
PARTICULAR merge would be defined, reproducible). The problem is however 
that we are dealing with ASYNCHRONOUS events. Real time isn't 
meaningful, just "states".

We start with one version of the data (initial state). We give this to 
two DISCONNECTED processes which can make changes. Afterwards we meant 
to return to one version of the data. It doesn't/shouldn't matter which 
process changed what and when during the time interval of separation. In 
general "which happens first" (which is SUPPOSED to happen first) is not 
well defined. That can be true even if the processes are running on the 
same multitasking computer --- it is what "queue on sharable resource" 
mechanisms are designed to mediate.

Imagine the following scenario. A (text) document is given to two 
workers to edit with instructions "get this job done by the end of the 
day". At this point your "merge" application is supposed to operate. You 
expect anything other than gobbly-gook for the result? You expect 
changes not to be lost? You are willing to accept different results 
depending upon when during the day the two workers chose to tackle their 
assignment? Understand now? While using something of the sort you 
describe would produce well defined results in terms of a PARTICULAR 
data merge it would not produce a defined resulting text from the 
defined "assignment" (if you tried again, since the two workers might 
next time choose different times during the day to perform the assigned 
task, the results would not be the same).

Michael