Thanks to the inheritance links, we are able to distinct the movies to its states. In these case, the addition of a new state does not imply code modification.
The VOD class manages its state thanks to an enumeration. In doing so, the solution imposes a ``switch'' statement, and so, the category changing is possible. The problem of this solution concerns the extensibility. Indeed, if a new category is added, the VOD class must be modified to manage the new type.