Different timing

Question

i have master -detail database blocks, in the detail i have field (ID) and i have start date for training and for how many days fields in master block.so let say the client has id (1234) take training on 22-nov-2009 for 3 days ...mean finished on 26-nov-2009 between 10:00 till 12:00. if the same client register in an another training in same days like 24-nov-2009 for 5 days from 11:00 till 15:00 (same timing)...should the system give message.
i wrote this code in (when-validate-item trigger) but it is not working ...
when-validate-item
============
begin
     SELECT count(*) into :global.dummy
     FROM PYPSTSM,PYPSTSD
     WHERE PYPSTSD_REF_NO = PYPSTSM_REF_NO
AND PYPSTSD_PARTICIPANT_PIDM = :PYPSTSD_PARTICIPANT_PIDM
AND :PYPSTSM_DATE BETWEEN PYPSTSM_DATE AND (((PYPSTSM_DATE+PYPSTSM_NO_OF_DAYS)-1))
AND (:PYPSTSM_START_TIME BETWEEN (PYPSTSM_START_TIME+(:PYPSTSM_START_TIME-PYPSTSM_START_TIME))
AND (PYPSTSM_START_TIME+(:PYPSTSM_START_TIME-PYPSTSM_END_TIME))
OR :PYPSTSM_END_TIME BETWEEN (PYPSTSM_END_TIME+(:PYPSTSM_END_TIME-PYPSTSM_START_TIME)) AND (PYPSTSM_END_TIME+(:PYPSTSM_END_TIME-PYPSTSM_END_TIME)))
AND PYPSTSD_STATUS_IND ='R';
if :global.dummy >0 then
message('*ERROR* this person has registered an another Training.');
message('*ERROR* this person has registered an another Training.');
RAISE FORM_TRIGGER_FAILURE;
end if;
end;

Answer 1

same result means what? Does it show your message? Does it not? Perhaps you could provide some sample data,here is mine
with data as (SELECT 10 STARTDATE, 12 ENDDATE, 1 ID FROM DUAL
              UNION ALL
              SELECT 12 STARTDATE, 13 ENDDATE, 2 ID FROM DUAL
              UNION ALL
              SELECT 13 STARTDATE, 15 ENDDATE, 3 ID FROM DUAL             
              UNION ALL
              SELECT 01 STARTDATE, 20 ENDDATE, 4 ID FROM DUAL             
              UNION ALL
              SELECT 01 STARTDATE, 10 ENDDATE, 4 ID FROM DUAL             
              UNION ALL
              SELECT 17 STARTDATE, 20 ENDDATE, 4 ID FROM DUAL             
SELECT * FROM DATA WHERE STARTDATE<=16 AND ENDDATE>=11
TARTDATE              ENDDATE                ID                    
10                     12                     1                     
12                     13                     2                     
13                     15                     3                     
1                      20                     4                     
4 rows selectedFor simplicity, i used numbers for the time