Only executing general page proces when action of button is validated

Question

I have a standard form and the standard buttons, create, delete, cancel and apply changes. Each button can have a condition, I checked those but I can't really do there what I wanted to do. So I looked to the process and found a plsql block could be used that returns a boolean.
So I came up with the following code, which does something, but isn't very much use(see below). The idea was that if I could only return one boolean then depending on the action it could be set to true or false, and return the boolean so the process could be done, or not. As I said, it does something, but not quite what I thought it may do, The only other way I could think of is to have separate processes for each button, but surely they wouldn't have included such a general process with those actions without a way of saying this action should only be executed then, this then and so on.
This is the code block, for whatever clarification it could bring:
DECLARE
-- booeland bestaat in plsql maar niet in sql
Waard varchar2(20);
teller number;
ingegevencode varchar2(1);
ingegevenapplicatiecd varchar2(25);
BEGIN
ingegevencode := 'S';
ingegevenapplicatiecd := 'Zesta';
select count(*) into teller from mailalertextbis where code = ingegevencode and applicatiecd = ingegevenapplicatiecd;
if teller >1 then
dbms_output.put_line('Er is een fout, deze mailalertbestaat 2 of meer keer');
waard := 'fout fout fout';
elsif teller = 1 then
if updating then
-- de bedoeling is dat if exist, door middel van select then
-- retrun true, otherwise false
waard := 'true';
elsif deleting then
-- then if not exists return false otherwise true
waard :='true';
elsif inserting then
waard :='false';
end if;
elsif teller = 0 then
if inserting then
waard := 'true';
elsif deleting then
waard := 'false';
elsif updating then
waard := 'false';
end if;
end if;
waard := 'niks ingevuld';
dbms_output.put_line('De waarde van waard is: ');
dbms_output.put_line(waard);
-- then if not exists return true otherwise false
END;

Answer 1

Can somebody please address this?
Thanks,