Here is a database schema concerning World War II warships. It involves the following relations:

Classes $($class$,$ type, country, guns, bore, displacement$)$

Ships $($ship$,$ class, launched$)$

Battles $($battle$,$ bdate$)$

Outcomes $($ship$,$ battle, result$)$

Ships are built in "classes" from the same design, and the class is usually named for the first ship of that class. The relation Classes records the name of the class, the type $(\text{'}$bb $\text{'}$ for battleship or $\text{'}$bc$\text{'}$ for battlecruiser$),$ the country that built the ship, the number of main guns, the bore $($diameter of the gun barrel in inches$)$ of the main guns, and the displacement $($weight$,$ in tons$).$ Relation Ships records the name of the ship, the name of its class, and the year in which the ship was launched. Relation Battles gives the name and date of battles involving these ships, and relation Outcomes gives the result $($sunk$,$ damaged, or ok$)$ for each ship in each battle.