Why do we need parkingDisplayBoard

Its very confusing article.Although classes are fine but the relation between them are really confusing.

  1. If each parking floor has display board that displays its information then if parking floor is fill, then what information does it displays?Because anyhow ticket will be allocated by system and it can be on different floor also.It need not to be on same floor.

  2. Why to display empty slot number of each type?What purpose does it solve as ticket will be assigned anywhere by system.