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Concepts of Database
Management, Fifth Edition
Chapter 7:
DBMS Functions
Objectives
7

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
7

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
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 Ensures
accuracy when several users update
database at same time
 Manages
complex scenarios for updates
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Figure 7.4: Ryan
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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 7
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
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Database before
updates
DBMS reads
database data into
RAM for Ryan
DBMS reads
database data into
RAM for Elena
Ryan changes
data in RAM
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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
 Use
shared update
batch processing
 Implement
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locking scheme
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Figure 7.7:
Delaying Updates
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Figure 7.8a:
Locking Scheme
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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: 7
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.)
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 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
 Recovery:
 Simplest
 Other
for recovering damaged database
return of database to correct state
recovery involves using backups
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
 Ease
for performance or other reasons
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
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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
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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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