In Figure 1-1, the elements drawn with dotted lines are the elements that must be modified or replaced when porting a ChorusOS operating system. Elements shown with unbroken lines are not usually changed when porting the system to another target.
DDI is the device driver interface. DKI is the device-kernel interface. Both these interfaces are described in detail in the ChorusOS 4.0 Device Driver Framework Guide. BKI is the boot-kernel interface. This is described in "The Boot-Kernel Interface (BKI)".