update employee assigment using api

Hi,

I have a requirement to update effective_start_date and effective_end_date for a particular person_id in the per_all_assignments_f table.

I've tried using hr_assignement_api with no luck.

DECLARE
--
l_cagr_grade_def_id number ;
l_cagr_concatenated_segments varchar2(240);
l_concatenated_segments varchar2(240);
l_soft_coding_keyflex_id number ;
l_comment_id number ;
l_effective_start_date date := '25-NOV-2007' ;
l_effective_end_date date := '12-DEC-2008' ;
l_no_managers_warning BOOLEAN ;
l_other_manager_warning BOOLEAN ;
l_hourly_salaried_warning BOOLEAN ;
l_gsp_post_process_warning varchar2(24);
--
l_es_NI varchar2(240);