Class data members have been discussed above in some detail, but nothing
has yet been said about how they are used. ADI allows procedures or
methods to be defined which can be overloaded on the basis of the
class of their arguments, ie. two methods can be defined with the
same name which have different arguments. 
ADI reserves some method names for its own
use for particular operations, and by specifying the Fortran subroutines
or C functions that will be called when these methods are required,
functionality is added to the ADI system. Not much more can be said
about methods for the moment until their place in the system becomes
apparent in the sections that follow.