SQL & PL/SQL :: Maintaining Aggregate Column Data Integrity?

What is the best practices to maintain aggregate columns? Suppose I have the following 2 tables:

DROP TABLE TEST.ORDERS_DET_T;
DROP TABLE TEST.ORDERS_T;
CREATE TABLE TEST.ORDERS_T (
ID NUMBER NOT NULL PRIMARY KEY,
ORDER_CODE VARCHAR2(100) NOT NULL,

[code]....

I want the following test script to act int the way, described in comments. Basically this means that the sum of TEST.ORDERS_DET_T.ORDER_DET_SUMA must be equal to TEST.ORDERS_T.ORDER_SUMA after transaction commits.

INSERT INTO TEST.ORDERS_T(ID, ORDER_CODE, ORDER_SUMA) VALUES(1,'FRUITS',100);
INSERT INTO TEST.ORDERS_DET_T(ID, ORDERS_T_ID, ORDER_DET_CODE, ORDER_DET_SUMA) VALUES(2,1,'APPLES',40);
INSERT INTO TEST.ORDERS_DET_T(ID, ORDERS_T_ID, ORDER_DET_CODE, ORDER_DET_SUMA) VALUES(3,1,'PEAT',60);
COMMIT; --SHOULD BE OK, 40+60=100

[code]....

P.S. Creating views based on ORDERS_T and ORDERS_DET_T are not an option, if the user would still be allowed to modify data in tables (as in test scenarios). This is because of current business situation, where the client has 2 teams (outsourcing for back-office solution and insourcing for web solution) that are accessing/modifying the data in the same tables.