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 Provide security services Provide data integrity features Support data independence Support data replication Provide utility services DBMS Functions 2

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 3

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 4

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

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 6

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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 14

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