The example projects have classes (such as OdExDgnSystemServices) which were derived from base classes with "Services" in their names. These are the platform-dependent parts of the system you intend to build. These classes provide services to your application, such as file i/o, font integration, and rendering. They are developed in the Dgn\Extensions\ExServices subdirectory.

OdRxSystemServices is the base class for classes that provide platform-dependent file operations. This provides access to finding, loading, and unloading modules, and creating and/or opening the specified files. Also, getting some options for the specified files and a message string format setting are possible through this class.

OdDgHostAppServices classes provide information about the program, version, preferable or substitute font, and progress (meter) monitoring.This class provides hints for finding SHX files, TTF files, image files, pattern (PAT) files, TX files (Teigha Xtension) and any referenced files. The class provides information typically used for populating the About dialog box information. Additionally, this is where functions are located to provide an UndoController to the application and to provide Warning and Error descriptions for the error codes.