Site grafting is one of the very powerful features of DPM where a site or site area may be virtually grafted to another site area. A grafted site framework will have consistent link/navigation management.
The DPM ContextEngine is the core component of DPM which supports and implements site grafting. To propertly setup WCM for using the ContextEngine follow the instructions in the this document:
DPM Context Engine - WCM Setup