Chapter 5

Data base Vs. File base

system
 Points should be covered

 File base vs. data base

 Advantages of data base
 Logical and Physical Views of Data
 Schemas, DBMS languages, Data dictionary
 Types of Files
Two basic types of files are used to store data.
1. The master file, which is conceptually similar
to a ledger in a manual system.
2. The transaction file, which is conceptually
similar to a journal in a manual system.
 File Approach
For many years, companies created new files and
programs each time an information need arose.
This proliferation(accumulation) of master files
created problems like:
1 Often the same data was stored in two or more
separate files.
2 The specific data values stored in the different files
were not always consistent.
 File-Oriented Approach
File 1
Fact A Sales
Fact B Program
Fact C
File 2
Fact B Shipping
Fact D Program
Fact E
File 3
Fact A Billing
Fact G Program
Fact E
 Databases
The database approach views data as an
organizational resource that should be used
by and managed for the entire organization,
not just the originating department or
function.
Its focus is data integration and data
sharing.
Integration is achieved by combining master
files into larger pools of data that can be
accessed by many application programs.
 Databases …
Database management system (DBMS) is the
program that manages and controls access to
the database.
A database management system serves as the
interface between the database and the various
application programs.
Database system is the combination of the
database, the DBMS and the application
program that uses the database.
Database administrator (DBA) is the person
responsible for the database.
 Database Approach
Database Sales Program

Fact A
Fact B Database
Shipping
management
Fact C Program
system
Fact D
Fact E Billing
Program
IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS

Database technology provides the following

benefits to organizations:
 Data integration • Achieved by combining
master files into larger
pools of data accessible
by many programs.
 IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS

Database technology provides the following

benefits to organizations:
 Data integration
 Data sharing • It’s easier to share data
that’s integrated.
 IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS

Database technology provides the following

benefits to organizations:
 Data integration
 Data sharing
 Reporting flexibility
• Reports can be revised easily and
generated as needed.
• The database can easily be browsed
to research problems or obtain
detailed information.
 IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS

Database technology provides the following

benefits to organizations:
 Data integration
 Data sharing
 Reporting flexibility
 Minimal data redundancy and
inconsistencies
• Because data items are
usually stored only once.
 IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS

Database technology provides the following benefits to

organizations:
 Data integration
 Data sharing
 Reporting flexibility
 Minimal data redundancy and inconsistencies
 Central management of data
• Data management is more efficient because the
database administrator is responsible for coordinating,
controlling, and managing data.
 IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS

Database technology provides the following

benefits to organizations:
• Relationships can be
 Data integration
explicitly defined and
 Data sharing used in the preparation
 Reporting flexibility of management
reports.
 Minimal data redundancy and inconsistencies
• EXAMPLE:
 Central management of data Relationship between
 Cross-functional analysis selling costs and
promotional
campaigns.
 Logical and Physical Views of Data

In file-oriented systems, programmers must know

the physical location and layout of records used
by a program.
They must reference the location, length, and
format of every field they utilize.
When data is used from several files, this
process becomes more complex.
 Logical and Physical Views of Data

Database systems overcome this problem by

separating the storage and use of data
elements.
Two separate views of the data are provided:
• Logical view
 How the user or programmer
conceptually organizes and
understands the data.
 Logical and Physical Views of Data

Database systems overcome this problem by

separating the storage and use of data elements.
Two separate views of the data are provided:
• Logical view
• Physical view

 How and where the data are

physically arranged and stored.
 Logical and Physical Views of Data

Database systems overcome this problem by

separating the storage and use of data elements.
Two separate views of the data are provided:
• Logical view
• Physical view
Separating these views facilitates application
development, because programmers can focus on
coding the logic and not be concerned with storage
details.
Logical View—User A Logical View—User B
Enrollment by Class Scholarship Distribution
Fr.
5%
Sr. Soph.
33% 24%

Jr.
38%

DBMS The DBMS

translates users’
logical views into
Operating
System
instructions as to
which data should
be retrieved from
Database the database.
Logical View—User A Logical View—User B
Enrollment by Class Scholarship Distribution
Fr.
5%
Sr. Soph.
33% 24%

Jr.
38%

DBMS The operating

system translates
DBMS requests
Operating
System into instructions to
physically retrieve
data from various
Database disks.
 Logical and Physical Views of Data

The DBMS handles the link between the

physical and logical views of the data.
Allows the user to access, query, and
update data without reference to how or
where it is physically stored.
The user only needs to define the logical
data requirements.
 Logical and Physical Views of Data

Separating the logical and physical views of

data also means users can change their
conceptualizations of the data relationships
without making changes in the physical
storage.
The database administrator can also change
the physical storage of the data without
affecting users or application programs.
 DATABASE SYSTEMS
Schemas
A schema describes the logical structure of a
database.
There are three levels of schema.
• Conceptual level schema
• The organization-wide view of the
entire database—i.e., the big picture.
• Lists all data elements and the
relationships between them.
 DATABASE SYSTEMS
Schemas
A schema describes the logical structure of a
database.
There are three levels of schema.
• Conceptual level schema
• External level schema
• A set of individual user views of portions of the
database, i.e., how each user sees the portion of
the system with which he interacts.
• These individual views are referred to as
subschema.
 DATABASE SYSTEMS
Schemas
A schema describes the logical structure of a
database.
There are three levels of schema.
• Conceptual level schema
• External level schema
• Internal level schema
• A low-level view of the database. Includes specific elements:
 Record layouts
 Definitions
 Addresses
 Indexes
 DATABASE SYSTEMS
An employee’s access to data should
be limited to the subschema of data
that is relevant to the performance of
his/her job.
 DATABASE SYSTEMS

The Data Dictionary

A key component of a DBMS is the data
dictionary.
• Contains information about the structure
of the database.
• For each data element, there is a
corresponding record in the data
dictionary describing that element.
 DATABASE SYSTEMS
Information provided for each element includes:
 A description or explanation of the element.
 The records in which it is contained.
 Its source.
 The length and type of the field in which it is
stored.
 The programs in which it is used.
 The outputs in which it is contained.
 The authorized users of the element.
 Other names for the element.
 DATABASE SYSTEMS

Accountants should participate in the

development of the data dictionary because
they have a good understanding of the data
elements in a business organization, as well as
where those elements originate and how they
are used.
 DATABASE SYSTEMS
DBMS Languages
Every DBMS must provide a means of
performing the three basic functions of:
• Creating a database
• Changing a database
• Querying a database
 DATABASE SYSTEMS
• DBMS Languages
Every DBMS must provide a means of
performing the three basic functions of:
• Creating a database
• Changing a database
• Querying a database
 DATABASE SYSTEMS
• Creating a database:
The set of commands used to create the
database is known as data definition language
(DDL). DDL is used to:
• Build the data dictionary
• Initialize or create the database
• Describe the logical views for each individual
user or programmer
• Specify any limitations or constraints on
security imposed on database records or fields
 DATABASE SYSTEMS
• DBMS Languages
Every DBMS must provide a means of
performing the three basic functions of:
• Creating a database
• Changing a database
• Querying a database
 DATABASE SYSTEMS
• Changing a database
The set of commands used to change the
database is known as data manipulation
language (DML). DML is used for
maintaining the data including:
• Updating data
• Inserting data
• Deleting portions of the database
 DATABASE SYSTEMS
• DBMS Languages
Every DBMS must provide a means of
performing the three basic functions of:
• Creating a database
• Changing a database
• Querying a database
 DATABASE SYSTEMS
• Querying a database:
The set of commands used to query the database is
known as data query language (DQL). DQL is used
to interrogate the database, including:
• Retrieving records
• Sorting records
• Ordering records
• Presenting subsets of the database
The DQL usually contains easy-to-use, powerful
commands that enable users to satisfy their own
information needs.
 DATABASE SYSTEMS
• Report Writer
Many DBMS packages also include a report writer, a
language that simplifies the creation of reports.
Users typically specify:
• What elements they want printed
• How the report should be formatted
The report writer then:
• Searches the database
• Extracts specified data
• Prints them out according to specified format
 DATABASE SYSTEMS

 Users typically have access to both DQL and

report writer.
 Access to DDL and DML are typically
restricted to employees with administrative
and programming responsibilities.
 End of ch5
• THE END OF CHAPTER ONE

Feb. 2014 Tamrat Ludego, Hawassa University 1 - 39