This document specifies a core semantic classification system of essential indoor features to describe indoor environments required commonly in various location-based indoor applications of buildings. The scope includes the following: —     semantic description of indoor features and their attributes; —     feature association between indoor features. The semantic classification system in this document is compatible with the building model defined in existing related standards. Geometric and topological descriptions of indoor features are not considered in this document. This document does not apply to other architectural structures, such as tunnels.