an association is a relationship between class that indicates some meaningful and interesting connection
do we need to remember what sale Line Item object are associated with a sale object
- yes because if not we would not be able to reconstruct a sale print a receipt of calculate a sale total
when to show an Association
on the other hand, a cashier may look up producteDescriptions, but there is no need to remember which particular chashier looks up partucular producteDescriptions