1. A computer-implemented building automation system (BAS) comprising: (A) A database adapted to store data definitions; (B) A relational directory of data definitions for the BAS stored in the database; and (C) An enterprise server engine, wherein the enterprise server engine is communicatively coupled to the database and adapted to manage the relational directory; the directory including: (D) A site level comprising at least one site definition, the site definition including a site description and a site manager description, wherein the site description relates a site with at least one portion of the BAS, and wherein the site manager description defines at least one site operation; (E) A system level comprising at least one system definition, wherein the system definition describes an association of a system with a site and an interaction of the system with at least one device comprising a portion of the BAS; (F) A device level comprising at least one device definition, wherein the device definition comprises a device behavior and functionality description, and relates a device with at least one site recognized by the BAS; and (G) An extension level comprising at least one extension definition, wherein each extension definition is associated with a device and defines an association of a device with at least one of a system, a site, or another device, such that the site level, the system level, the device level, and the extension level are organized in a hierarchical relationship in the database; (H) wherein the enterprise server engine is adapted to automatically configure the database without a user providing new information in response to discovery by the enterprise server engine of a previously unknown device not described in the database.