Use Case #8. POS server provides data
You have a server with data from your POS to be integrated with srv4pos.com where your server is a source of the articles/sales and srv4pos.com is the destination.
To send taxes, categories, products and commodities data to srv4pos.com see Use Case #2. Simple Articles provder.
To provide sales use mecahnism used at Use Case #5. Regular POS.