The size, material, type and direction of the opening of a door are always coherent with its function. A door can be like a transparent diaphragm that separates the dining area from the living room, as in the first immages; can blend with the wall in which it is, to hide a closet, like in the second example; can be decorated with precious materials and signalize the exit, like in the third case, or can get to separate three different rooms (living room-corridor-kitchen), as proposed in the last example.