tagCategory: specifies whether the type (class or enumeration) is considered as universal, application, or private.
universal: this refers to types recognized as part of the SAIF standard. It includes the basic data types (e.g. String, Integer, etc.), the constructor classes (e.g. Tuple, Set, etc.), and the higher-level SAIF classes (e.g. SpatialEntity, Coordinate, etc.).
application: this refers to types used by the user, which are outside of the SAIF standard and which exist as part of a widely used schema, such as NTDB. The assignment of application tags is governed by a central authority.
private: this class refers to types defined by the user which are outside the SAIF standard and outside the scope of the application tagCategory as defined above. (A fourth tagCategory is calculated. This is of no direct interest to the user. It is used in the binary encoding of certain geometric constructs in the SAIF schema.)
tagNumber: a unique number within a tagCategory which can be used to identify the type.
The values for universal and application tagCategory/tagNumber are unique; i.e., each universal or application tagCategory/tagNumber corresponds to exactly one subclass. Since the use of private tags is unrestricted, values for tagCategory/tagNumber are not guaranteed to be unique. Consequently, within any transfer the user must ensure that private tag numbers are unique.