Some use cases:
multimap
- With ZIP code as a key, all people which have that ZIP code
- With account ID as key, all open orders of that person/account
- A dictionary, with per keyword various explanations
multiset
is in essence a map with a key and a integer count.
- The inventory of a shop, all products have their key and the amount
still available is the value
- accumulated sales data of a shop, every time a product is sold the
product id get's added to the multiset thereby increasing the amount sold