To delete pending leaves

To delete pending leaves
As far as i know there is no API to delete pending leaves.

Solution1:
This is my own way of deleting the leaves

CREATE OR REPLACE PROCEDURE xx_delete_pending_leaves
AS
   CURSOR c1
   IS
      SELECT hat.transaction_id, hats.transaction_step_id
        FROM hr_api_transactions hat, hr_api_transaction_steps hats
       WHERE hat.transaction_ref_table = 'PER_ABSENCE_ATTENDANCES'
         AND hat.transaction_group = 'ABSENCE_MGMT'
         AND hat.transaction_identifier = 'ABSENCES'
         AND hat.transaction_ref_id IS NOT NULL
         AND hat.status = 'Y'
         AND hat.transaction_id = hats.transaction_id;
--For a particular employee/pass the person_id values as a cursor parameter
         --AND hat.CREATOR_PERSON_ID = 11923;
   --AND hats.creator_person_id = p_person_id;  -- Add date conditon later and person ID if required

   l_transaction_id        NUMBER;
   l_transaction_step_id   NUMBER;
   l_error                 VARCHAR2 (300);
BEGIN
   OPEN c1;
   LOOP
      FETCH c1
       INTO l_transaction_id, l_transaction_step_id;
      EXIT WHEN c1%NOTFOUND;
      IF l_transaction_step_id IS NOT NULL
      THEN
         DELETE FROM hr_api_transaction_values
               WHERE transaction_step_id = l_transaction_step_id;
         DBMS_OUTPUT.put_line
                     (   'Deleted Transaction Value of transaction step id: '
                      || l_transaction_step_id
                     );
      END IF;

      IF l_transaction_id IS NOT NULL
      THEN
         DELETE FROM hr_api_transaction_steps
               WHERE transaction_id = l_transaction_id;
         DBMS_OUTPUT.put_line
                           (   'Deleted Transaction step of transaction id: '
                            || l_transaction_id
                           );

        DELETE FROM hr_api_transactions
               WHERE transaction_id = l_transaction_id;

        DBMS_OUTPUT.put_line ('Deleted Transaction ID: ' || l_transaction_id);
      END IF;
   END LOOP;

   CLOSE c1;
   COMMIT;
EXCEPTION
   WHEN OTHERS
   THEN
      l_error := SUBSTR (SQLERRM, 1, 200);
      DBMS_OUTPUT.put_line (   'Other Error in xx_delete_pending_leaves- '
                            || l_error
                           );
--p_out := 'Other Error in xx_delete_pending_leaves- '||l_error; -- Removed OUT parameter
-- Write FND_LOG for concurrent program log
END xx_delete_pending_leaves;

Solution 2:
We can enable/disable the update/delete icon in Absence Management - HR self service responsibility. How ?
Solution: Get query from jsp page (OAF) (See Standard Query below) and change the decode value of cancel_icon, Confirm_icon and update_icon values by passing 'HrCancelEnabled/HrCancelDisabled' OR 'HrUpdateEnabled/HrUpdateDisabled' values and replace with the custom query.

Tables Used in Standard Query are:
        per_absence_attendances,
       per_absence_attendance_types,
       per_abs_attendance_types_tl,
       hr_lookups,
       hr_api_transactions,
       hr_api_transaction_steps

Standard Query:

SELECT  NVL(paa.date_start,paa.date_projected_start) start_date
        ,NVL(paa.date_end,paa.date_projected_end) end_date
       ,paattl.name absence_type
       ,paat.absence_attendance_type_id absence_attendance_type_id
       ,fcl.meaning  absence_category
       ,paat.absence_category  absence_category_code
       ,paa.absence_hours
       ,(SELECT meaning from hr_lookups where 'A' = lookup_code(+) and 'LEAVE_STATUS' = lookup_type(+))
       approval_status
       , 'A' approval_status_code
       ,decode(paa.date_start,null,
                                   (SELECT meaning from fnd_lookup_values
                                    where lookup_type ='ABSENCE_STATUS' and lookup_code ='PLANNED'
 and language = userenv('LANG')),
                                   (SELECT meaning from fnd_lookup_values
                                    where lookup_type ='ABSENCE_STATUS' and lookup_code ='CONFIRMED'
and language = userenv('LANG')))
        absence_status
       , decode(paa.date_start,null,'PLANNED','CONFIRMED') absence_status_code
       ,(nvl((SELECT 'Y'
     from fnd_attached_documents
     where entity_name='PER_ABSENCE_ATTENDANCES'
     and pk1_value = to_char(paa.absence_attendance_id) and rownum = 1),'N')) supporting_documents
       ,decode (
        paa.date_start,null,
        decode(paa.date_projected_start, null, 'HrCancelDisabled', 'HrCancelEnabled'),
          decode(
               sign(trunc(paa.date_start)-trunc(sysdate)),1,'HrCancelEnabled',
                                                                              decode(paa.date_end,null,'HrCancelEnabled','HrCancelDisabled')
              )
       )
        cancel_icon
       ,decode(paa.date_end,NULL,
          decode(paa.date_start,Null, 'HrConfirmEnabled','HrConfirmDisabled'), 'HrConfirmDisabled' )
         confirm_icon      
       ,decode ( paa.date_start,null,
          'HrUpdateEnabled',
           decode(sign(nvl(paa.date_end,sysdate+1)-sysdate),1,'HrUpdateEnabled','HrUpdateDisabled'))
         update_icon              
       ,NULL
         details_icon
       ,paa.absence_attendance_id
       ,null transaction_id
      ,to_char(paa.absence_attendance_id) supportingDocKey
      ,paa.absence_days
FROM  per_absence_attendances paa
     ,per_absence_attendance_types paat
     ,per_abs_attendance_types_tl paattl
     ,hr_lookups fcl
WHERE 1=1
 and paa.person_id = :1
      and paa.business_group_id+0 = :2
      and paa.absence_attendance_type_id = paat.absence_attendance_type_id
      and paat.absence_attendance_type_id = paattl.absence_attendance_type_id
      and paattl.language = userenv('LANG')
      and fcl.lookup_type(+) = 'ABSENCE_CATEGORY'
      and paat.absence_category = fcl.lookup_code(+)
      and ((hr_api.return_legislation_code(paat.business_group_id) = 'GB'
         and nvl(paat.absence_category,'#')  not in
('M','GB_PAT_ADO','GB_PAT_BIRTH','GB_ADO'))
         or
       (hr_api.return_legislation_code(paat.business_group_id) <> 'GB'
         and nvl(paat.absence_category,'#') not in
('GB_PAT_ADO','GB_PAT_BIRTH','GB_ADO')))
      and not exists
      ( select 'e'
        from hr_api_transactions t
         WHERE
        t.selected_person_id = paa.person_id
        and t.CREATOR_PERSON_ID  = nvl(:3,t.CREATOR_PERSON_ID)
       and t.transaction_ref_table='PER_ABSENCE_ATTENDANCES'
         and t.transaction_ref_id = paa.absence_attendance_id
         and not(hr_absutil_ss.getabsencetype(t.transaction_id,    NULL) IS NULL
         and t.status = 'W')
         and t.status not in ('D','E')
      )
union all
select hr_absutil_ss.getStartDate(hat.transaction_id,null) start_date
       ,hr_absutil_ss.getEndDate(hat.transaction_id,null) end_date
      ,hr_absutil_ss.getAbsenceType(hat.transaction_id,null) absence_type
       , to_number(hats.Information5) absence_attendance_type_id
      ,hr_absutil_ss.getAbsenceCategory(hat.transaction_id,null)  absence_category
      , hats.Information6 absence_category_code
       ,hr_absutil_ss.getAbsenceHoursDuration(hat.transaction_id,null)  absence_hours
       ,hr_absutil_ss.getApprovalStatus(hat.transaction_id,null) approval_status
       ,hr_absutil_ss.getApprovalStatusCode(hat.transaction_id,null) approval_status_code
       ,hr_absutil_ss.getAbsenceStatus(hat.transaction_id,null) absence_status
       , hats.Information9 absence_status_code
       ,hr_absutil_ss.hasSupportingDocuments(hat.transaction_id,hat.TRANSACTION_REF_ID) supporting_documents
       ,hr_absutil_ss.isCancelAllowed(hat.transaction_id,null,hat.status) cancel_icon
       ,hr_absutil_ss.isConfirmAllowed(hat.transaction_id,null) confirm_icon
     ,hr_absutil_ss.isUpdateAllowed(hat.transaction_id,null,hat.status) update_icon
       ,null  details_icon
      ,hat.TRANSACTION_REF_ID absence_attendance_id
       ,hat.transaction_id transaction_id      
       ,to_char(hat.TRANSACTION_REF_ID||'_'||hat.transaction_id) supportingDocKey
      ,hr_absutil_ss.getAbsenceDaysDuration(hat.transaction_id,null)  absence_days          
from hr_api_transactions hat
     ,hr_api_transaction_steps hats
where hat.TRANSACTION_REF_TABLE='PER_ABSENCE_ATTENDANCES'
and hat.TRANSACTION_GROUP='ABSENCE_MGMT'
and hat.TRANSACTION_IDENTIFIER='ABSENCES'
and hat.TRANSACTION_REF_ID is not null
--and hat.SELECTED_PERSON_ID =:4
--and hat.CREATOR_PERSON_ID  = nvl(:5,hat.CREATOR_PERSON_ID)
and hat.transaction_id=hats.transaction_id(+)
and hat.status not in ('D','E')
and not (hr_absutil_ss.getabsencetype(hat.transaction_id,null) is null and hat.status='W')

To get pending leaves

      SELECT hat.transaction_id, hats.transaction_step_id
        FROM hr_api_transactions hat, hr_api_transaction_steps hats
       WHERE hat.transaction_ref_table = 'PER_ABSENCE_ATTENDANCES'
         AND hat.transaction_group = 'ABSENCE_MGMT'
         AND hat.transaction_identifier = 'ABSENCES'
         AND hat.transaction_ref_id IS NOT NULL
         AND hat.status = 'Y'
         AND hat.transaction_id = hats.transaction_id
         AND hat.CREATOR_PERSON_ID = :p_person_id; 

To get approved leaves

         SELECT pat.NAME absence_type, paa.date_start leave_start_date,
                paa.date_end leave_end_date, paa.absence_days, paa.abs_information_category,
                paa.abs_information2, paa.abs_information3,paa.abs_information4
           FROM per_absence_attendances paa,
                per_absence_attendance_types pat,
                per_all_people_f papf
          WHERE paa.absence_attendance_type_id =
                                                pat.absence_attendance_type_id
            AND papf.person_id = paa.person_id
            AND TRUNC (paa.date_start) BETWEEN TRUNC
                                                    (papf.effective_start_date)
                                           AND TRUNC (papf.effective_end_date)
            AND TRUNC (p_date) BETWEEN TRUNC (paa.date_start)
                                   AND TRUNC (NVL (paa.date_end,
                                                   paa.date_start
                                                  )
                                             )
            AND papf.person_id = :p_person_id;