Azrina, suppose you have 2 tables:
ACCOUNT (Parent Table)
ACCOUNT-TRANSACTION (Dependent Table, because every transaction must be associated to one account. To ensure this relation, an referential integrity rule without "cascade" option has been defined).
To delete one row from ACCOUNT table, all the dependents rows in ACCOUNT_TRANSACTION must be deleted first. With "cascade" option, when parent row is deleted, all dependents rows are automaticly deleted too.
I hoped this help you.
Regards, ALF.