Records exist containing the Dow Jones Industrial Average closing price for each date the stock exchange was open.

A symbol table could be constructed with key = date and value = closing price.

An interactive application could use this table simply to report the closing price for any date input. But if the date (the key) is not in the table, it would be nice for the application to report the "next" date the exchange was open and the closing price for that date instead of simply reporting that the exchange was closed on the original input date.