File update


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File update

Updating a file.

A frequently performed operation on files is the updating of a master file using a transaction file.

A master file is a large semi-permanent file which contains some data that may change whenever a transaction takes place. These transactions are stored on a temporary small file called a transaction file, and this is used to update the master file after a certain period has elapsed (at the end of each day / week etc).

It is important that the master file and the transaction file are sorted on the same key field.

The system flow chart for the process is shown below:

There are two input files :

The Old Master File
The Transaction File (sorted)

And one output file :

The New Master File.

The pseudocode for the update process is as follows :

open master file;
create new master file;
open transaction file;
while not eof(transaction file) do
	read record from transaction file;
	repeat
		read record from master file;
		if not matching record then write master record to new master file;
	until master and transaction records match;
	update master record;
	write updated master record to new master file;
end while;
copy remaining master file records to new master file;
close all files;