In sylius, one order has many shipments. I find this strangule. In real life aren't they One-to-One relationship ? Thank you for your explication.
Currently there is only one. But in the future, there will be many. You can for example have multiple devilery addresses, or admin stuff decide to send some of ordered items via different shipping method under same order.
So, this many-to-one gives you flexibility and is investment into the future. Same with payments.