Database concepts

Introduction to Database Concepts
Ucc - Mwanza.
May 2006

Database Definition
A database can be defined as collection
of information organized in such a way
that it can be accessed easily.
Examples are
 Tracking customer orders
 Maintaining Employees Records.
 Maintaining Students Information

Terminologies
In studying Databases the following Terminologies
must be clear
Data
 This is the fact or facts about specific entity (person, place or thing).
Information
 This is the processed facts perceived to be useful by the user.
Field
 This is a single item of information or data in entity. E.g. employee
Name
Record
 This can be defined as data or group of fields about an
entity. E.g. employee particulars
Subject (relation or table)
 This can be defined as a collection of records that are related
to a particular entity. For example, Records for all employees
will make up one subject.

History of Databases
Manual systems
File Processing Systems (FPS)
Database Management systems
(DBMS)

Manual systems
Structure
Information can be stored in dedicated room or in separate offices.
Room or office will be furnished with shelves;
Different shelves will hold Records for different subjects.
Records will be stored in hard flat files, each file will carry one record
Each file will have a specific number to identify it.
A person will use the file number to retrieve the specific file (record).

Manual systems
User
File keeper
Files Cabinet

File Processing Systems (FPS)
Information stored as groups of records in separate
files
File processing systems consisted of a few data files
and many application programs
Each file called a soft flat file
Flat file contain processed information for one specific
function
Use of programming languages to write applications
Little flexibility
High maintenance
Many limitations

Limitations of File Processing Systems
Separate and isolated data
Data redundancy
Program - data interdependence
involving file formats and access
techniques
Difficulty in representing data from the
user’s view
Data inflexibility

Database Management systems (DBMS)
A program that allows users to define, create, manipulate,
store, maintain, retrieve, and process the data in a
database in order to produce meaningful information.
Focus on information representation
Data stored as records in various database files that can
be combined to produce meaningful information for users
DBMS controls all functions of capturing, processing,
storing, retrieving data and generates various forms of
data output
Manages access by multiple users and multiple programs
to a common store of data

DBMS overcomes all Limitations of FPS.
Eliminates separation and isolation of data
Reduces data redundancy
Eliminates dependence between programs
and data
Allows for representation of data from user’s
view
Increases data flexibility
Superior flexibility and security over
spreadsheet applications

Characteristics of a DBMS
 Computerized record-keeping system
 Contains facilities that allow the user to:
o Add, delete files
o Insert, retrieve, update, delete data
 Collection of databases; each can be
used for separate purposes or
combined

Functions and Uses of a DBMS
To store data
To organize data
To control access to data
To protect data
To provide decision support
To provide transaction processing

Advantages and Disadvantages of a DBMS
• Advantages:
 Centralized data reduces management problems
 Data redundancy and consistency are controllable
 Program - data interdependency is diminished
 Flexibility of data is increased
• Disadvantages:
 Reduction in speed of data access time
 Requires special knowledge
 Possible dependency of application programs to specific
DBMS versions

Database Administrator
A database administrator (DBA) controls and
manages the database.
Function of a DBA
Make decisions concerning the content of the
database
Plan storage structures and access strategies.
Provides support to users
Defines security and integrity checks
Interprets backup and recovery strategies.

Types of Databases
Flat Databases
Hierarchical Database
Network Database
Relational Database

Flat databases
A single kind of record with a fixed number
of fields.
a way of organizing all information in a
single table.
suitable for extremely simple
databases.
inherit data redundancy

Hierarchical Database
Fields or records structured in nodes
Viewed as branches of an upside-down tree
Each item is subordinate to its parent node
Only one parent per node
The subordinate item is the child node to the parent
If parent node is deleted, all the child nodes are as well
deleted
New parent node must be created before adding a new child
node
Limited by rigid structure
No direct relationships between child nodes

Network Database
Also has hierarchical node arrangement
But here child nodes may have more than
one parent node, or a many-to-many
relationship
The interconnected design allows for access
via multiple pathways

Relational Database
No pre-determined access paths
Data stored in a collection of columns and
rows called a table, or a relation
Tables may be electronically linked via a
key field containing common data
Easy to add, delete and modify the data and
the table structures

Relational Terminologies
Table or Relation
Null values
Duplicate Values
Changeable Values
Primary Keys
Foreign Keys

Table or Relation
Table will store information for a
particular entity
Table name must be unique
The Table name should be descriptive
Column Name must be unique within
the Table
Rows must be unique

Null values
missing or unknown value in a column
of a table
Nulls are not the same as zeros
Most arithmetic operations can be
performed on zero values
nulls must be excluded from
mathematical manipulations

Duplicate values
A duplicate value is a value in a column
of a table that exactly matches some
other values within the same column.

Changeable values
value in a table that may vary over time.
Most values in most tables are
Changeable
You can prevent changes when it is
desirable to prevent changes in a given
column of a table

Primary keys
Uniquely identify each row of that table.
Every table must have only one
Primary key

Rules for Primary key
Must always have a value (null values
are not allowed)
Value should be unique (duplicate
values are not allowed)
Value should not change over time

Foreign keys
key which relates the rows of the Table
to other Tables
value can be null,
value can change
value can be duplicated

Rule for Foreign keys
Value must refer to the existing primary
key.

Database concepts

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