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

Concepts of Database Concepts of Database Management, Fifth Management, Fifth

EditionEdition

Chapter 7:Chapter 7:

DBMS FunctionsDBMS Functions

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Concepts of Database Management, 5th Edition

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

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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

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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

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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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Figure 7.1: Adding Record

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Figure 7.2:Updating Record

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Figure 7.3: Retrieving Data

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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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Support Concurrent Update

Ensures accuracy when several users update database at same time

Manages complex scenarios for updates

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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

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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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Figure 7.6a: Lost Update

Database before updates

Ryan changes data in RAM

DBMS reads database data into RAM for Elena

DBMS reads database data into RAM for Ryan

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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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Avoiding Lost Updates

Prohibit shared update

Use batch processing

Implement locking scheme

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Figure 7.7: Delaying Updates

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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

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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

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Figure 7.8b: Locking Scheme (con’t.)

DBMS updates database with Elena’s change

DBMS unlocks record

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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

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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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Figure 7.9: Deadlock

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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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Figure 7.12: Forward Recovery

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Figure 7.13:Backward Recovery

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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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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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Figure 7.21: Integrity Constraints in a DBMS

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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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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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Figure 7.22:Replicas From Master Database

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Figure 7.23:DBMS Synchronizes Databases

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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

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Provide Utility Services (con’t.)

Provide support for embedded procedures

Procedural

Nonprocedural

Provide easy-to-use, menu-driven interface

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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

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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

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