Our shipping company operates a line of container ships. We know the number of containers each ship can hold. Each container is identified by an industry-standard code. Containers are brought to ships and taken from ships by specially designed trucks. We track the latitude and longitude of each truck and each ship. Each truck is identified by our own naming system. While in transit, each container is either on a ship or on a truck. For each container, we know the customer name. The entities are Container, Ship, and Truck