A CDF must be created by the CDF library. In a C application CDFs are created using either the CDFcreate function (Standard Interface) or the <CREATE_,CDF_> operation of the CDFlib function (Internal Interface). In a Fortran application CDFs are created using either the CDF_create subroutine (Standard Interface) or the <CREATE_,CDF_> operation of the CDF_lib subroutine (Internal Interface).