synchronise virtuemart with and external database

[manue]

hello

i am working on a shoponline with joomla2.5 and virtuemart 2.
my walk-in store and e-shop will share the same stock of products.
so i need to make sure that stock is adjusted appropriately for both the physical  walk-in store and the ecommerce everytime time a product is sold.
I am thinking talend or any other ETL ? but its asynchronous - the update needs to be done on a real time basis
I am thinking webservices ?
need it both ways - on event : update of database 1 has to activate the same update on database 2 and this both ways, which will lead to a nonsense as update on db2 will activate update on db1 and so on
I am pretty sure that the solution exists but can't find anything

[jenkinhill]

Have you thought about using a VM POS  like http://forum.virtuemart.net/index.php?topic=118401.0