This class diagram is split into three parts: building, controller and filter. The building, which is being described more precisely in Building, contains the construction of a building with its rooms, components and notifications. The controllers are there to handle API requests and control change of the building. Filters are units which filter a collection of objects of the building construction. Everything is being controlled by the BuildingManager unit.
A description of the identification number called "in" in this diagram can be found in the Ubiquitous Language.