Answers
Such as the customer or warehouse
The entities in the scenario
The document or details being transferred
The source and destination entities
An arrow comes back the other way
The people, departments or organisations involved
Message travels in one direction only
Name written on each flow line
Receiver gives no reply
One arrow from source to destination
Reply follows the first message
A to B then B to A
Such as an invoice
No arrow comes back
The content of each message
Shown as boxes, ellipses or circles
Messages travel in both directions
Customer orders, gets nothing back
Two arrows between the same points