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The following examples are
typical declarative business rules, and show how they are
seamlessly translated into the rule-based technology.
Example Rule 1
A Customer cannot withdraw money if their account is overdrawn
or the account has been frozen.
The precise conditions are: the sum of the TRANSACTIONS is less
than 0 or the ACCOUNT_STATUS is Frozen.
Implementation:
SELECT '' RESTRICT
FROM ACCOUNT
A
WHERE 0 > (
SELECT SUM(T.TXN_AMOUNT)
FROM TRANSACTIONS T
WHERE A.ACCOUNT_ID =
T.ACCOUNT_ID)
OR
A.ACCOUNT_STATUS = 'FROZEN'
This business rule is a
restrictive type of
constraint. It affects two database objects. This rule would ensure
that the situation (described above) would never be possible.
This business rule is checked
regardless how these transactions enter the system (e.g. direct
entry, background process, or batch process).
Also, this business rule is
checked regardless of how the rule is broken (e.g. adding a new
transaction, changing the amount of any transaction, or setting the
account to frozen).
Example Rule 2
Customers are charged an ATM transaction fee of $1.00. If the
customer has generated more than 10 ATM transactions since the last
statement, ATM transaction fees would be waived.
Implementation:
INSERT INTO
TRANSACTION_FEES
(ACCOUNT_ID,TXN_AMOUNT,TXN_DATE,TXN_FEE_ID)
SELECT
ACCOUNT_ID,1,SYSDATE,1
FROM TRANSACTIONS
T
WHERE OLD(TXN_ID)
IS NULL
AND 10 >
( SELECT COUNT(*)
FROM TRANSACTION_FEES TF,
ACCOUNT A
WHERE TF.TXN_DATE >
A.LAST_STATEMENT_DATE
AND TF.ACCOUNT_ID =
A.ACCOUNT_ID
AND TF.ACCOUNT_ID =
T.ACCOUNT_ID)
This Rule is behavioral,
corrective. If a transaction is generated, then the Rule will check
to see if 10 transaction fees have already been created since the
last statement date. If less than 10 have been created, the Rule
will create a new transaction fee to go along with the transaction
the user has just entered.
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