1. Principles of Database Design, Conclusions AIMS 2710 R. Nakatsu

2. Integrity of a Database It is important that the data in a database is correct and consistent. Data integrity problems can occur due to: n incorrect data entry n data redundancy n poor database design

3. Ways to Maintain Data Integrity n Entity Integrity (primary key must be unique and must not be null) n Referential Integrity n Field types (e.g., text, numeric, date, yes/no) n Input masks (e.g., ISBN numbers, dates) n Field validation rules (What are some examples?) n Good design of input screens (user interfaces) n Check digits

4. User Interface Design © 2000 Prentice Hall

5. Check Digit Example  Add a check digit to validate a clerk’s data entry.  The check digit is determined by some mathematical algorithm. Example: Multiply the first digit by 2; multiply the second digit by 3; multiply the third by 4; add the results; divide by 10 and take the remainder. 127 yields (1*2 + 2*3 + 7*4) / 10 = 36 / 10 for a check digit of 6.

6. Concurrency Control Concurrency control is the management of concurrent transaction execution. Why is it important? The simultaneous execution of transactions over a shared database may create several data- integrity and consistency problems.

7. Lost Updates: An Example Note that the first transaction has not been permanently recorded when the second transaction is executed.

8. Concurrency Control with Locking A lock guarantees exclusive use of a data item to a current transaction. In the previous example, transaction T2 will not have access to the data item that is currently used by transaction T1. The lock is released when the transaction T1 is completed.

9. Data Warehouse n support OLAP (online analytical processing) n support data mining (data in a data warehouse are analyzed to reveal hidden patterns and trends in historical business activity) stores data that have been extracted from the various operational, external, and other databases of an organization Data warehouses...

10. Data Warehouse

11. Recap n Why do we need a database? n What is a database? n What are the main functions of a DBMS? n Entity-Relationship Modeling n Linking two tables: 1:1, 1:many, many:many n Data Integrity n Concurrency Control n Data Warehouses