1. A computer-implemented system for facilitating cross-subsystem queries of a plurality of building automation subsystems, comprising: an ontology database storing an ontological model for a building automation system (BAS), wherein the ontological model defines multiple different BAS object types, relationships between the BAS object types, and attributes of the BAS object types; a fact database storing instance values for the plurality of building automation subsystems and a logical type for each of the stored instance values, wherein the logical type identifies a particular attribute of the ontological model described by the stored instance value and represents, in a flat format, a portion of the ontological model that provides semantic type information for the stored instance value; and a query engine configured to decompose a cross-subsystem query received from an application into a plurality of subsystem queries using information of the fact database, wherein the query engine parses the logical types in the fact database to obtain the semantic type information for the stored instance values and uses the obtained semantic type information to identify one or more of the stored instance values relevant to the cross-subsystem query without requiring access to another database.