PostgreSQL - regularly sync.ing remote and local data

We are developing an application for leather industry using PostgreSQL with
PHP scripting. The program will be run from a central server and buyers and
sellers will login using internet connection and update/exchange information
through the system.

Some companies do not want to be connected to the internet throughout the
day. They want to use the system from a local server during the day and
update the data to the central server (and get the updated data from the
server) once or twice a day.

Can someone please advise me, how this can be accomplished? That is, to make
the two databases hand shake and exchange the changes effected since they
last met.

Best regards,


Siva,
Chennai, Tamil Nadu