In older versions of Building Applications, the variable BB_FLOORMASTER_DGN defined the what BB_FloorMaster.dgn was active. Within this file the various Floor Definitions were defined. When launching the Floor Manager, the actual BB_FloorMaster.dgn was entered. That is, the active file became the FloorMaster. This was obvious as the background became blue, and red rectangles appeared, displaying the defined Floors. Some users had a tendency to work within this file, Reference other Files, accidentally leaving Geometry. By doing this there was often cases of corruption within the FloorMaster.dgn.
In ABD (AECOsim Building Designer), the same variable, BB_FLOORMASTER_DGN, now defines the BB_FloorMaster.dgnlib, where the Floors are defined. In ABD, when launching the Floor Manager you remain in the current dgn, but are able to modify your Floor Definitions, writing to the FloorMaster, without the threat of accidental corruption.