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The University of Akron Dept of Business Technology Computer Information Systems 2440: 180 Database Concepts Instructor: Enoch E. Damson DBMS Functions • • • • • • • • • 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 Functions of a DBMS 2 Update and Retrieve Data • 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 • Fundamental capability of a DBMS 3 Provide Catalog Services • Stores metadata (data about other data) • Often hidden from users • Used by database administrators and programmers DBMS Functions • Contains descriptions of database components • Data dictionary in larger DBMSs 4 Support Concurrent Update • Manages complex scenarios for updates DBMS Functions • Ensures accuracy when several users update database at same time 5 Avoiding Lost Updates • Ways to avoid lost updates include the following: • 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 • Prohibit shared update 6 Locking Schemes • Two-Phase Locking • Locks are held until required updates completed • 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 • Deadlock 7 Locking Schemes… • Timestamping • Avoids the need to lock rows DBMS Functions • DBMS assigns each database update a unique time when the update started • Eliminates processing time needed to apply and release locks • Helps detect and resolve deadlocks 8 Recovery • Mechanism for recovering damaged database • Recovery: return of database to correct state • Other recovery methods: • Journaling – maintaining a journal (log) of updates DBMS Functions • Simplest recovery involves using backups • Forward recovery – applies after images of updates • Backward recovery – applies before images of updates 9 Provide Security Services • 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 DBMS Functions • Prevention of unauthorized access • Views – snapshort of data in a database • Privacy – right of individuals to have certain information kept confidential 10 Provide Data Integrity Features • 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 • Rules followed to ensure data is accurately and consistently updated • Key integrity 11 Support Data Independence • Programs must be independent of database structure • Adding a field • Changing length of field DBMS Functions • Considerations • Creating an index • Adding or changing a relationship 12 Support Data Replication • Maintained for performance or other reasons • Ease of access and portability DBMS Functions • Manage multiple copies of same data in multiple locations 13 Provide Utility Services • Assist in general database maintenance • Permit addition and deletion of indexes • Provide access to operating system services DBMS Functions • Permit changes to database structure • Support for queries, screen generators, and report generators 14 Provide Utility Services… • Provide support for embedded procedures • Nonprocedural • Provide easy-to-use, menu-driven interface DBMS Functions • Procedural 15
