1. Concepts of Database Management, Fifth Edition
Chapter 7:
DBMS Functions

2. Objectives Introduce the functions, or services, provided by a DBMS
Describe how a DBMS handles updating and retrieving data
Examine the catalog features of a DBMS
Illustrate the concurrent update problem and describe how a DBMS handles this problem
Explain the data recovery process in a database environment
Concepts of Database Management, 5th Edition

3. Objectives Describe the security services provided by a DBMS
Examine the data integrity features provided by a DBMS
Discuss the extent to which a DBMS achieves data independence
Define and describe data replication
Present the utility services provided by a DBMS
Concepts of Database Management, 5th Edition

4. Nine Functions of a DBMS
Update and retrieve data
Provide catalog services
Support concurrent update
Recover data
Provide security services
Provide data integrity features
Support data independence
Support data replication
Provide utility services
Concepts of Database Management, 5th Edition

5. Update and Retrieve Data
Fundamental capability of a DBMS
Users don’t need to know how data is stored or manipulated
Users add, change, and delete records during updates
Users view and manipulate data during retrieval
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6. Figure 7.1: Adding Record
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7. Figure 7.2: Updating Record
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8. Figure 7.3: Retrieving Data
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9. Provide Catalog Services
Stores data about data
Contains descriptions of database components
Often hidden from users
Used by database administrators and programmers
Data dictionary in larger DBMSs
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10. Support Concurrent Update
Ensures accuracy when several users update database at same time
Manages complex scenarios for updates
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11. Figure 7.4: Ryan Updates the Database
Before update
DBMS reads data from database into RAM for Ryan
Ryan changes data in RAM
DBMS updates database with Ryan’s change
Concepts of Database Management, 5th Edition

12. After Ryan’s update and before Elena’s
Figure 7.5: Elena Updates the Database
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
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13. Database before updates
Figure 7.6a: Lost Update
Database before updates
DBMS reads database data into RAM for Ryan
DBMS reads database data into RAM for Elena
Ryan changes data in RAM
Concepts of Database Management, 5th Edition

14. Figure 7.6b: Lost Update (con’t.)
Elena updates data in RAM
DBMS updates database with Ryan’s change
DBMS updates database with Elena’s change; Ryan’s update is lost!
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15. Avoiding Lost Updates Prohibit shared update Use batch processing
Implement locking scheme
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16. Figure 7.7: Delaying Updates
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17. Figure 7.8a: Locking Scheme
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
Concepts of Database Management, 5th Edition

18. Figure 7.8b: Locking Scheme (con’t.)
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
Concepts of Database Management, 5th Edition

19. Figure 7.8b: Locking Scheme (con’t.)
DBMS updates database with Elena’s change
DBMS unlocks record
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20. Locking Schemes Two-Phase Locking Deadlock Locking on PC-Based DBMSs
Locks are held until required updates completed
Deadlock
Occurs when two users hold a lock and require a lock on the resource that the other already has
DBMS chooses method to break deadlock
One user becomes ‘victim’
Locking on PC-Based DBMSs
Table or row locked, not both
Usually more limited than locking facilities on mainframe DBMSs
Concepts of Database Management, 5th Edition

21. Locking Schemes (con’t.)
Timestamping
DBMS assigns each database update a unique time when the update started
Avoids the need to lock rows
Eliminates processing time needed to apply and release locks
Helps detect and resolve deadlocks
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22. Figure 7.9: Deadlock
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23. Recovery Mechanism for recovering damaged database
Recovery: return of database to correct state
Simplest recovery involves using backups
Other recovery methods:
Journaling
Forward recovery
Backward recovery
PC-based
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24. Figure 7.12: Forward Recovery
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25. Figure 7.13: Backward Recovery
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26. Provide Security Services
Prevention of unauthorized access
Encryption - converts data to indecipherable form
Authentication - identification of DBMS user, often with passwords or biometrics
Authorizations - rules to specify data available to certain users
Views
Privacy
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27. Provide Data Integrity Features
Rules followed to ensure data is accurately and consistently updated
Key integrity
Foreign key and primary key constraints
Data integrity
Data type
Legal values
Format
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28. Figure 7.21: Integrity Constraints in a DBMS
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29. Support Data Independence
Programs must be independent of database structure
Considerations
Adding a field
Changing length of field
Creating an index
Adding or changing a relationship
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30. Support Data Replication
Manage multiple copies of same data in multiple locations
Maintained for performance or other reasons
Ease of access and portability
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31. Figure 7.22: Replicas From Master Database
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32. Figure 7.23: DBMS Synchronizes Databases
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33. Provide Utility Services
Assist in general database maintenance
Permit changes to database structure
Permit addition and deletion of indexes
Provide access to operating system services
Support for queries, screen generators, and report generators
Concepts of Database Management, 5th Edition

34. Provide Utility Services (con’t.)
Provide support for embedded procedures
Procedural
Nonprocedural
Provide easy-to-use, menu-driven interface
Concepts of Database Management, 5th Edition

35. Summary A DBMS provides update and data retrieval functions
DBMS catalog service
Support concurrent update
Prevent shared update, locking systems, timestamp updates
Recovery services allow a database to overcome unexpected failures
Concepts of Database Management, 5th Edition

36. Summary
Security Services ensure users don’t have access to data they are not authorized to view, update or delete
Data replication services allow you to maintain copies of the data closer to where you use it or to provide for disaster recovery
Your DBMS will provide a set of utility services, such as reporting and access to operating system services
Concepts of Database Management, 5th Edition