Abstract: A mechanism for locating and calling an appropriate member function to process a message or command in an event-based system is provided. An object data structure contains data members and a pointer to a virtual function table. The virtual function table contains pointers to member functions associated with the object. The virtual function table contains a pointer to a member function that returns the address of a message map. The message map contains two entries: a pointer to a base message map and a pointer to an array of message map entries. The array of message map entries contains the addresses and parameters of member functions. A default window procedure member function searches the array of message map entries to locate a desired member function. If the desired member function is not located in the array of message map entries for the derived class, then the window procedure member function searches the array of message map entries for the base class of the derived class.