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Chapter 9
Database
Management
Systems
1
Objectives for Chapter 9
 Problems in the flat-file approach to data management
Why these gave rise to the database concept
 Relationships among the elements of the database environment
 Characteristics of the relational database model
 Three stages in database design including
Conceptual design
Logical design
Physical design
 Anomalies caused by unnormalized databases and the need for data
normalization
 Features of distributed databases
Considerations in deciding on a particular database
configuration
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Flat-File Versus Database
Environments
 Computer processing involves two components: data
and instructions (programs).
 Conceptually, there are two methods for designing the
interface between program instructions and data:
File-oriented processing: A specific data file was
created for each application
Data-oriented processing: Creates a single data
repository to support numerous applications
 Disadvantages of file-oriented processing include
redundant data and programs and varying formats for
storing the redundant data.
 The format for similar fields may vary because the
programmer used inconsistent field formats.
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Flat-File Environment
User 1
Transactions
Data
Program 1
A,B,C
User 2
Transactions
Program 2
X,B,Y
User 3
Transactions
Program 3
L,B,M
Data Redundancy &
Flat-File Problems
Data Storage - creates excessive storage
costs of paper documents and/or magnetic
form
Data Updating - any changes or additions
must be performed multiple times
Currency of Information - potential problem
of failing to update all affected files
Task-Data Dependency - user’s inability to
obtain additional information as his or her
needs change
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Database Approach
User 1
Transactions
Database
Program 1
User 2
Transactions
Program 2
User 3
Transactions
Program 3
D
B
M
S
A,
B,
C,
X,
Y,
L,
M
Advantages of the
Database Approach
Data sharing/centralize database resolves flat-file problems:
 No data redundancy - Data is stored only once, eliminating
data redundancy and reducing storage costs.
 Single update - Because data is in only one place, it
requires only a single update procedure, reducing the time
and cost of keeping the database current.
 Current values - A change to the database made by any
user yields current data values for all other users.
 Task-data independence - As users’ information needs
expand beyond their immediate domain, the new needs can
be more easily satisfied than under the flat-file approach.
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Disadvantages of the
Database Approach
Can be costly to implement
additional hardware, software, storage, and
network resources are required
Can only run in certain operating
environments
may make it unsuitable for some system
configurations
Because it is so different from
the file-oriented approach, the database
approach requires training users
may be inertia or resistance
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Elements of the Database Approach
System Development
Process
Database
Administrator
Applications
Transactions
U
S
E
R
S
Transactions
Transactions
User
Programs
User
Programs
User
Programs
User Queries
DBMS
Data
Definition
Language
Data
Manipulation
Language
Query
Language
Host
Operating
System
Physical
Database
DBMS Features
User Programs - make the presence of the DBMS
transparent to the user
Direct Query - allows authorized users to access
data without programming
Application Development - user created
applications
Backup and Recovery - copies database
Database Usage Reporting - captures statistics on
database usage (who, when, etc.)
Database Access - authorizes access to sections of
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the database
Internal Controls and
DBMS
The purpose of the DBMS is to provide
controlled access to the database.
The DBMS is a special software system
programmed to know which data
elements each user is authorized to
access and deny unauthorized
requests of data.
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Data Definition Language
(DDL)
DDL is a programming language used to define
the database to the DBMS.
The DDL identifies the names and the relationship of
all data elements, records, and files that constitute
the database.
Viewing Levels:
internal view - physical arrangement of records
(1)
conceptual view - representation of database
(1)
user view - the portion of the database each
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user views (many)
ANSI Model
External
User Views
Conceptual
Model
Internal
Model
Physical
Database
Data Manipulation
Language (DML)
DML is the proprietary programming
language that a particular DBMS uses to
retrieve, process, and store data.
Entire user programs may be written in
the DML, or selected DML commands can
be inserted into universal programs, such
as COBOL and FORTRAN.
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Query Language
The query capability permits end users
and professional programmers to access
data in the database without the need for
conventional programs.
IBM’s Structured Query Language (SQL)
is a fourth-generation language that has
emerged as the standard query language.
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Three Steps in Designing
a Database
Prepare the conceptual model
Identify the entities
Identify the relationships between the entities
Prepare the ER diagram
Specify the logical design
Select the logical database model (relational)
Transform the conceptual data model using a
logical database model
Implement the physical design
Physical structures
Access methods
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Phase 1
Prepare the Conceptual
Model
Draw an ERD to
capture the
process.
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ER-Diagram Symbols
ER-Diagram Symbols
Entity
Primary Key
Relationship
Attribute
Example of a Relationship Linking
Two Entities
CUSTOMER
1
M
places
Order Number
Name
Number
ORDER
Item #
An Entity
...is an
individual object
concept
event
...may be a specific
tangible object
intangible object
Entity Class is a collection of entities with
similar attributes.
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Attributes
A property of an entity that we choose to record (of
interest to an organization).
CUSTOMER (entity)
PRODUCT (entity)
customer #
product #
name
description
address
finish
telephone no.
price
balance
qty. on hand
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Cardinalities
Entity
Salesperson
Relationship
1
1
Customer
Vendor
M
Assigned
Places
Supply
Entity
1
M
M
Car
Order
Inventory
ER-Diagram using REA Model
R
Inventory
E
M
Line items
M
A
M
Sales
1
Party to
M
Sales
person
M
1
Pays for
Made to
Customer
1
M
M
1
Cash
Increases
M
Cash
Collections M
Received
from
1
Received
by
Cashier
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Phase 2
Specify the Logical
Design
Create relational
tables.
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Logical Data Structures
A particular method used to organize records
in a database is called the database’s
structure.
The objective is to develop this structure
efficiently so that data can be accessed
quickly and easily.
Four types of structures are:
hierarchical (AKA the tree structure)
network
relational
object-oriented
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The Relational Model
The relational model portrays data in the
form of two dimensional tables:
relation - the database table
attributes (data elements) - form
columns
tuples (records) - form rows
data - the intersection of rows and columns
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RESTRICT - filtering out rows,
such as the purple
PROJECT - filtering out columns,
such as the purple
JOIN
X1
Y1
Y1
Z1
X1
Y1
Z1
X2
Y2
Y2
Z2
X2
Y2
Z2
X3
Y1
Y3
Z3
X3
Y1
Z1
Properly Designed Relational Tables
No repeating values - All occurrences at
the intersection of a row and column are a
single value.
The attribute values in any column must all
be of the same class.
Each column in a given table must be
uniquely named.
Each row in the table must be unique in at
least one attribute, which is the primary key.
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Relational Model Data
Linkages (>1 table)
 No explicit pointers are present. The data are viewed as a
collection of independent tables.
 Relations are formed by an attribute that is common to
both tables in the relation.
 Assignment of foreign keys:
if 1 to 1 association, either of the table’s primary keys may
be the foreign key.
if 1 to many association, the primary key on one of the
sides is embedded as the foreign key on the other side.
if many to many association, may embed foreign keys or
create a separate linking table.
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Three Types of Anomalies
 Insertion Anomaly: A new item
cannot be added to the table until
at least one entity uses a
particular attribute item.
 Deletion Anomaly: If an
attribute item used by only one
entity is deleted, all information
about that attribute item is lost.
 Update Anomaly: A modification
on an attribute must be made in
each of the rows in which the
attribute appears.
 Anomalies can be corrected by
creating relational tables.
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Advantages of Relational
Tables
Removes all three anomalies
Various items of interest (customers,
inventory, sales) are stored in separate
tables.
Space is used efficiently.
Very flexible. Users can form ad hoc
relationships.
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The Normalization Process
A process which systematically splits
unnormalized complex tables into
smaller tables that meet two conditions:
all nonkey (secondary) attributes in the table
are dependent on the primary key
all nonkey attributes are independent of the
other nonkey attributes
When unnormalized tables are split and
reduced to third normal form, they must
then be linked together by foreign keys.
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Steps in Normalization
Table with
repeating groups
Remove
repeating
groups
First normal
form 1NF
Remove
partial
dependencies
Second normal
form 2NF
Third normal
form 3NF
Higher normal
forms
Remove
transitive
dependencies
Remove
remaining
anomalies
Accountants and Data
Normalization
The update anomaly can generate conflicting and
obsolete database values.
The insertion anomaly can result in unrecorded
transactions and incomplete audit trails.
The deletion anomaly can cause the loss of
accounting records and the destruction of audit
trails.
 Accountants should have an understanding of the
data normalization process and be able to
determine whether a database is properly
normalized.
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Phase 3
Implement the Physical
Design
Decide about
software and
hardware.
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Physical Database Design
Transition from theoretical to physical
aspects of database
IS  IT
Decisions about software and hardware
Implementation
Populate the database with data
Produce physical user views (multiple)
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Data Structures
allow records to be located, stored, and
retrieved and allow movement through
the database. Two components:
The organization of a file is the physical
arrangement of records.
The access method is the technique used
to locate records and to navigate through the
database.
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Distributed Data
Processing
Central
Site
Site A
Centralized
Database
Site B
Site C
Distributed Data
Processing
DP is organized around several
information processing units (IPUs)
distributed throughout the organization
and placed under the control of the
end users.
DDP does NOT mean
Decentralization!
IPUs are connected to
one another and
coordinated.
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Potential Advantages of
DDP
Cost reductions in hardware and data
entry tasks
Improved cost control responsibility
Improved user satisfaction since
control is closer to the user level
Backup of data can be improved
through the use of multiple data storage
sites
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Potential Disadvantages of
DDP
Loss of control
Mismanagement of organization-wide
resources
Hardware and software incompatibility
Redundant tasks and data
Consolidating incompatible tasks
Difficulty attracting qualified personnel
Lack of standards
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Centralized Databases in DDP
Environment
The data is retained in a central
location.
Remote IPUs send requests for data.
Central site services the needs of the
remote IPUs.
The actual processing of the data is
performed at the remote IPU.
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Data Currency
Occurs in DDP with a centralized database
During transaction processing, the data
will temporarily be inconsistent as a
record is being read and updated.
Database lockout procedures are
necessary to keep IPUs from reading
inconsistent data and from writing over a
transaction being written by another IPU.
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Distributed Databases:
Partitioning
Splits the central database into segments that
are distributed to their primary users
Advantages:
users’ control is increased by having data
stored at local sites
transaction processing response time is
improved
the volume of transmitted data between IPUs is
reduced
reduces the potential data loss from a
disaster
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The Deadlock Phenomenon
Especially a problem with partitioned
databases
Occurs when multiple sites lock each
other out of data that they are currently
using
One site needs data locked by another site.
Special software is needed to analyze and
resolve conflicts.
Transactions may be terminated and have to be
restarted.
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The Deadlock Phenomenon
Locked A, waiting for C
Locked E, waiting for A
A,B
E, F
C,D
Locked C, waiting for E
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Distributed Databases:
Replication
The duplication of the entire
database for multiple IPUs
This method is effective for situations with
a high degree of data sharing, but no
primary user, and supports read-only
queries.
The data traffic between sites is reduced
considerably.
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Concurrency Problems and
Control Issues
Database concurrency is the presence
of complete and accurate data at
all IPU sites. With replicated
databases, maintaining current data at
all locations is a difficult task.
Time stamping may be used to
serialize transactions and to prevent
and resolve any potential conflicts
created by updating data at various
IPUs.
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