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The University of Akron Dept of Business Technology Computer Information Systems

The University of Akron Dept of Business Technology Computer Information Systems. DBMS Functions. 2440: 180 Database Concepts Instructor: Enoch E. Damson. Functions of a DBMS. Update and retrieve data Provide catalog services Support concurrent update Recover data

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The University of Akron Dept of Business Technology Computer Information Systems

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  1. The University of AkronDept of Business TechnologyComputer Information Systems DBMS Functions 2440: 180Database Concepts Instructor: Enoch E. Damson

  2. 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 DBMS Functions

  3. 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 DBMS Functions

  4. Provide Catalog Services • Stores metadata (data about other data) • Contains descriptions of database components • Often hidden from users • Used by database administrators and programmers • Data dictionary in larger DBMSs DBMS Functions

  5. Support Concurrent Update • Ensures accuracy when several users update database at same time • Manages complex scenarios for updates DBMS Functions

  6. Avoiding Lost Updates • Ways to avoid lost updates include the following: • Prohibit shared update • Use batch processing – a single update program reads the batch of records in a file one at a time and performs the appropriate updates to the database, periodically • Implement locking scheme – denies other users access to data while the DBMS processes another user’s updates to the database DBMS Functions

  7. Locking Schemes • Two-Phase Locking • 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 DBMS Functions

  8. Locking Schemes… • 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 DBMS Functions

  9. Recovery • Mechanism for recovering damaged database • Recovery: return of database to correct state • Simplest recovery involves using backups • Other recovery methods: • Journaling – maintaining a journal (log) of updates • Forward recovery – applies after images of updates • Backward recovery – applies before images of updates DBMS Functions

  10. Provide Security Services • Prevention of unauthorized access • Encryption - converts data to indecipherable form • Authentication - identification of DBMS user, often with passwords, biometrics, smart cards • Authorizations - rules to specify data available to certain users using • Four parts of authorization rule include: • Subject, object, action, and constraint • Views – snapshort of data in a database • Privacy – right of individuals to have certain information kept confidential DBMS Functions

  11. 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 – field value must be consistent with data type • Legal values – specific values for fields • Format – special entry and display formats DBMS Functions

  12. 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 DBMS Functions

  13. Support Data Replication • Manage multiple copies of same data in multiple locations • Maintained for performance or other reasons • Ease of access and portability DBMS Functions

  14. 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 DBMS Functions

  15. Provide Utility Services… • Provide support for embedded procedures • Procedural • Nonprocedural • Provide easy-to-use, menu-driven interface DBMS Functions

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