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

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

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

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

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 Concepts of Database Management, 5th Edition

Figure 7.1: Adding Record Concepts of Database Management, 5th Edition

Figure 7.2: Updating Record Concepts of Database Management, 5th Edition

Figure 7.3: Retrieving Data Concepts of Database Management, 5th Edition

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 Concepts of Database Management, 5th Edition

Support Concurrent Update Ensures accuracy when several users update database at same time Manages complex scenarios for updates Concepts of Database Management, 5th Edition

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

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 Concepts of Database Management, 5th Edition

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

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! Concepts of Database Management, 5th Edition

Avoiding Lost Updates Prohibit shared update Use batch processing Implement locking scheme Concepts of Database Management, 5th Edition

Figure 7.7: Delaying Updates Concepts of Database Management, 5th Edition

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

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

Figure 7.8b: Locking Scheme (con’t.) DBMS updates database with Elena’s change DBMS unlocks record Concepts of Database Management, 5th Edition

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

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 Concepts of Database Management, 5th Edition

Figure 7.9: Deadlock Concepts of Database Management, 5th Edition

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 Concepts of Database Management, 5th Edition

Figure 7.12: Forward Recovery Concepts of Database Management, 5th Edition

Figure 7.13: Backward Recovery Concepts of Database Management, 5th Edition

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 Concepts of Database Management, 5th Edition

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 Concepts of Database Management, 5th Edition

Figure 7.21: Integrity Constraints in a DBMS Concepts of Database Management, 5th Edition

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 Concepts of Database Management, 5th Edition

Support Data Replication Manage multiple copies of same data in multiple locations Maintained for performance or other reasons Ease of access and portability Concepts of Database Management, 5th Edition

Figure 7.22: Replicas From Master Database Concepts of Database Management, 5th Edition

Figure 7.23: DBMS Synchronizes Databases Concepts of Database Management, 5th Edition

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

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

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

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