In Odoo ERPOnline, you can define several bills of materials for the same product. In fact, you can have several manufacturing methods or several approved raw materials for a given product. You will see in the following section that the manufacturing procedure (the routing) is attached to the Bill of Materials, so the choice of bill of materials implicitly includes the operations to make it.
Once several bills of materials have been defined for a particular product, you need to have a system to enable Odoo ERPOnline to select one of them for use. By default, the bill of materials with the lowest sequence number is selected by the system.