Relations between Places

Being an Entity, a Place may be contained in another Place. This is a current situation in the real world. For instance a city contains a lot of houses each of one being a Place. If P1 contains P2, each Entity contained in P2 is contained in P1 by transitity. By this mean, it is possible to create a Place that contains all Places (i.e. all Entities) in a World. We call such a Place a Root-Place

Places may be contiguous too. There are for example rooms in a house.

But a Place can never intersect another one. This is an implementation issue: an Entity can never be in several Places at the same time.