What's the difference between item supplier associations and the approved supplier list?

Item supplier associations indicate the supplier and address from which an item is supplied and the item organization to which it's supplied. You create these associations by editing an item in the Product Information Management work area.

The approved supplier list is where you define your approved suppliers, sites, and other information for procuring specified items. You create entries on this list with the Manage Approved Supplier List Entries task in the Purchase Orders and Purchase Agreements work areas. Suppliers themselves are created in the Suppliers work area.