1. Constraints

2. Primary Key Constraint
It is derived from the entity UID or created as surrogate key.
Uniqueness is enforced by an index:
Index is not defined in Oracle Designer
All columns in key are mandatory.
It should not be updatable.
Every table should have one!

3. Unique Key Constraint Derived from secondary entity UIDs
Can include NULL columns
Are optional
Recommended where a surrogate key is used for PK

4. Foreign Key Constraint
Derived from relationships
Can reference either a primary or a unique key:
But avoid referencing unique keys!
Must not be partly NULL
Can reference its own table
Cannot reference tables on other databases

5. Foreign Key Rules X Server handles RESTRICT and CASCADE Delete only
NULLIFY
DEFAULT
(default)
TITLE
RENTAL
COPY
COPY
DML X
DML
DML
DML
DML
NULL
DEFAULT
RENTAL_ITEM
COPY
BOOKING
BOOKING
Server handles RESTRICT and CASCADE Delete only

6. Defining Foreign Key Rules
Foreign Key Properties
Cascades
Defaults
Nullifies
Restricted
Cascade Rules
Delete Rule
Update Rule
Avoid using any update rule:
PKs should not be updatable

7. Check Constraint
CHECK ((position = 'TECHNICAL' AND salary BETWEEN 3000 AND 4000) OR
(position != 'TECHNICAL'))
EMPLOYEES
IDENTIFIER
LAST_NAME
FIRST_NAME
POSITION
SALARY

8. Foreign Keys in Arcs CHECK ((FK_A IS NOT NULL AND FK_B IS NULL)
DSD1 A ID C ID
FK_A
FK_B B ID
CHECK ((FK_A IS NOT NULL AND
FK_B IS NULL)
OR (FK_B IS NOT NULL AND
FK_A IS NULL))

9. Implementing Subtypes
GAME and MOVIE subtypes in TITLES
TITLES
PRODUCT_CODE
TI_TYPE
CHECK ((TI_TYPE = 'GA' AND
GAME_CATEGORY IS NOT NULL AND
MEDIUM IS NOT NULL AND
MOVIE_CATEGORY IS NULL AND
AGE_RATING IS NULL)
OR ...
TITLE
MOVIE_CATEGORY
AGE_RATING
GAME_CATEGORY
MEDIUM

10. More Uses for Check Constraints
START_DATE < END_DATE
Positive numeric column values > 0
IS NOT NULL
Can only check columns within the same row; use triggers for more complex checks

11. Defining a Check Constraint
Create Check Constraint for EMPLOYEES : Name
Check constraint name
Check constraint condition
Column
EMP_DEPT_FK
Specify the Where/Validation condition

12. Where Are Constraints Validated?
At the client, the server or both
Considerations:
Database integrity
Interactive response
Network traffic
Overall system performance

13. Specifying Location of Validation
Relational Table Definitions
Foreign Keys
BOO_COP_FK
Where to enforce
Foreign Key Properties
Validation
Validate in
Client
Server
Both
None

14. Action Edit Block Field
Server Validation
Client
Server
Action Edit Block Field
Customers:
DML Posted
Guaranteed integrity
Minimal network traffic
No immediate feedback

15. Server and Client Validation
Action Edit Block Field
Customers:
DML Posted
Guaranteed integrity
Immediate feedback
Network traffic for every check

16. Action Edit Block Field
Client Validation
Client
Server
Action Edit Block Field
Customers:
DML Posted
Immediate feedback
No guaranteed integrity
Network traffic for every check
and again for DML or commit

17. Guidelines for Choosing Where to Validate
Server validation:
Guaranteed data integrity
Client and server validation:
Check constraints
Lookup foreign keys +
Case-by-case basis:
Other foreign keys
Unique keys ? +
Lesson Aim
<Enter lesson aim here.>

18. Controlling When to Enforce
Client
Action Edit Block Field
Customers:
Transaction Committed
Server
Typical transactions:
Oracle validates each DML statement.
Complex transactions:
Oracle8 server can defer validation until COMMIT.

19. Specifying When Validation Occurs
Relational Table Definitions
Foreign Keys
BOO_COP_FK
Foreign Key Properties
Validation
Defer Status
INITIALLY DEFERRED
INITIALLY IMMEDIATE
NOT DEFERRED
When to enforce

20. Summary Constraints enforce data integrity:
Entity integrity
Referential integrity
Arcs, subtypes, and simple business rules
Validation can be carried out:
Server and client
Deferred