1 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Chapter 7 DBMS Functions

2 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Objectives u Introduce the functions, or services, provided by a DBMS u Describe how a DBMS handles updating and retrieving data u Examine the catalog features of a DBMS u Illustrate the concurrent update problem and describe how a DBMS handles this problem u Explain the data recovery process in a database environment

3 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Objectives u Describe the security services provided by a DBMS u Examine the data integrity features provided by a DBMS u Discuss the extent to which a DBMS achieves data independence u Define and describe data replication u Present the utility services provided by a DBMS

4 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Nine Functions of a DBMS u Update and retrieve data u Provide catalog services u Support concurrent update u Recover data u Provide security services u Provide data integrity features u Support data independence u Support data replication u Provide utility services

5 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Update and Retrieve Data u Fundamental capability of a DBMS u Users don’t need to know how data is stored or manipulated u Users add, change, and delete records during updates u Users view and manipulate data during retrieval

6 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Adding Record Figure 7.1

7 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Updating Record Figure 7.2

8 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Retrieving Data Figure 7.3

9 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Provide Catalog Services u Stores data about data u Contains descriptions of database components u Often hidden from users u Used by database administrators and programmers u Data dictionary in larger DBMSs

10 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Support Concurrent Update u Ensures accuracy when several users update database at same time u Manages complex scenarios for updates

11 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Ryan Updates the Database Figure 7.4 Before update DBMS reads data from database into RAM for Ryan Ryan changes data in RAM DBMS updates database with Ryan’s change

12 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Elena Updates the Database Figure 7.5 After Ryan’s update and before Elena’s DBMS reads database data into RAM for Elena Elena changes data in RAM DBMS updates database with Elena’s change

13 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Lost Update Figure 7.6a Database before updates Ryan changes data in RAM DBMS reads database data into RAM for Elena DBMS reads database data into RAM for Ryan

14 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Lost Update (con’t.) Figure 7.6b Elena updates data in RAM DBMS updates database with Ryan’s change DBMS updates database with Elena’s change; Ryan’s update is lost!

15 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Avoiding Lost Updates u Prohibit shared update u Use batch processing u Implement locking scheme

16 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Delaying Updates Figure 7.7

17 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Locking Scheme Figure 7.8a Database before updates DBMS reads database data into RAM for Ryan and locks record Elena requests same record and request fails Ryan changes data in RAM; Elena’s request for same record again fails

18 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Locking Scheme (con’t.) Figure 7.8b DBMS updates database with Ryan’s change; Elena’s request for same record again fails DBMS unlocks record; DBMS reads database data into RAM for Elena and locks record Elena changes data in RAM

19 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Locking Scheme (con’t.) Figure 7.8b DBMS updates database with Elena’s change DBMS unlocks record

20 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Locking Schemes u Two-Phase Locking l Locks are held until required updates completed u Deadlock l Occurs when two users hold more than one lock at a time l DBMS chooses method to break deadlock l One user becomes ‘victim’ u Locking on PC-Based DBMSs l Table or row locked, not both l Usually more limited than locking facilities on mainframe DBMSs

21 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Locking Schemes (con’t.) u Timestamping l DBMS assigns each database update a unique time when the update started l Avoids the need to lock rows l Eliminates processing time needed to apply and release locks l Helps detect and resolve deadlocks

22 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Deadlock Figure 7.9

23 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Recovery u Mechanism for recovering damaged database u The return of database to correct state is called recovery u Simplest recovery involves using backups u Other recovery methods l Journaling l Forward recovery l Backward recovery l PC-based

24 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Forward Recovery Figure 7.12

25 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Backward Recovery Figure 7.13

26 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Provide Security Services u Prevention of unauthorized access l Encryption - converts data to indecipherable form l Authentication - identification of DBMS user, often with passwords or biometrics l Authorizations - rules to specify data available to certain users l Views u Privacy

27 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Provide Data Integrity Features u Rules followed to ensure data is accurately and consistently updated u Key integrity l Foreign key and primary key constraints u Data integrity l Data type l Legal values l Format

28 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Integrity Constraints in a DBMS Figure 7.21

29 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Support Data Independence u Programs must be independent of database structure u Considerations l Adding a field l Changing length of field l Creating an index l Adding or changing a relationship

30 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Support Data Replication u Manage multiple copies of same data in multiple locations u Maintained for performance or other reasons u Ease of access and portability

31 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Replicas From Master Database Figure 7.22

32 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski DBMS Synchronizes Databases Figure 7.23

33 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Provide Utility Services u Assist in general database maintenance u Permit changes to database structure u Permit addition and deletion of indexes u Provide access to operating system services u Support for queries, screen generators, and report generators

34 7 Concepts of Database Management, 4 th Edition, Pratt & Adamski Provide Utility Services (con’t.) u Provide support for embedded procedures l Procedural l Nonprocedural u Provide easy-to-use, menu-driven interface