Internal mapping files are prepared by the SDNF interface administrator. They tell the interface where on the computer network the external mapping files may be found. The format of internal mapping files is described. Refer to Internal Mapping Files for further information.

External mapping files are files which determine how the interface handles the data for going to the target package, or coming from the source package; for example, the Profile, Profile Orientation, Unicode and Material mapping files. The format of the external mapping files is described. Refer to External Mapping Files for further information.

Overloading of mapping files is permitted and may occur. A file that is found in the first folder is overwritten by a file with the same identifying characteristics, though not necessarily with the same filename (refer to Internal Mapping Files for further information), found later in any of the succeeding folders. For example, a project mapping file can overload a company mapping file.

The sequence of environment variables is set to the locations of the internal mapping files. The interface searches all the folders pointed to by these variables and locate all files with the suffix .map in each sub-folder called SDNFMaps. The .map files are imported during system initialisation as internal mapping files. The internal mapping files then become the basis for locating the external mapping files.