Consider a scenario of selling houses. There is a multiple listing service $($MLS$)$ that provides information about homes for sale. A unique MLS number is assigned to the listing, along with the date and price of the listing. Other required properties to post the listing include the address $($street$,$ city, state, zip$)$ and the listing agent with realty.

The MLS must also maintain a history of price changes, which is displayed on the Web page with the date and price on that date.