Database Reference

Order Split keeps Magento sales orders unchanged and adds a small registry that records which orders were created from the same checkout.

Relationship Why it matters
sales_order_split_order belongs to one sales_order_split_group Groups all child orders created by the same split operation.
sales_order_split_order points to one sales_order Connects the split registry to the standard Magento order.

Order items, invoices, shipments and payments continue to use Magento's normal sales records. Integrations can use the registry to find related orders without replacing Magento's order model.