pos intergration with existing data

I require an touch screen POS that will use the product data from my existing website mysql database. The inventory will be kept up to data in the existing database. This would be probably be achieved by using existing open source POS and either:- 1. full intergration with existing database or 2. both databases running separately and a script running every 5 - 15 min that would update the inventories in each database dependent on if date/time last updated more recent than last update. this script would also add any new items from the existing database to the POS database.