To have a floor implies that there is a place above the floor. A floor is a base and a lower limit, but it is also the support for whatever exists above it. One definition describes a floor as the part of a room on which one stands. I question that the enclosure of walls and ceiling is necessary. Even if there is no other containment, the space above a floor is charged with the expectation of what will happen or the memory of what has happened on it. Another definition of floor describes it as the ground on which people move about. The floor is qualified by the activity it supports.