The BASED ON clause lets you extract from the database the
    data type and size of a field and then use it to declare host
    language types. These are Pascal TYPE(s), and C typedef(s). When
    you preprocess your program, the RDML preprocessor assigns the
    data type and size attributes associated with the field to the
    variable or function you declare using the the BASED ON clause.

    See the DECLARE_VARIABLE statement for information on declaring
    host language variables.