I'm missing some cardinalities. A relationship can be optional on both sides, optional on one side and mandatory on the other, or mandatory on both sides.
For example order 1..* ------ 0..* item.
left: an order is about one or more items (zero not possible -> mandatory)
right: an item does not have to be on an order, but there can be more than one on an order
Maybe some inspiration to enhance the possibilities are found on