Ongoing Warehouse pulls article registry updates from PrestaShop to the WMS. PrestaShop contains the master data.
The WMS downloads new and updated orders which are not yet handled. If an order is updated, the change is transferred unless the warehouse workers have started working on it. When orders are fulfilled, the WMS marks the order as completed (A history row are added to Prestashop and the current status is changed.).
Stock balance is sent from Ongoing Warehouse to PrestaShop. The WMS should be master data when it comes to available stock. This is especially important if you sell across multiple channels.
The integration uses PrestaShop's web service.