This illustration:
http://docs.oasis-open.org/ubl/os-UBL-2.1/art/UBL-2.1-OrderingProcess.png

• The arrow from "Accept order" to "order canceled" indicates accepted orders end up in a cancelled state without any notification (yes, it says "[response not required]".) In a process supporting responses and changes as outlined should the process after "Accept order" be to return response.
• The arrow from "Add detail" to "Accept order" should be removed and "Add detail" should be be "Update and accept order".

We may add a simpler process with less responses to indicate a lighter implementation.