Introduction to Database Concepts
Ucc - Mwanza.
A database can be defined as collection
of information organized in such a way
that it can be accessed easily.
Tracking customer orders
Maintaining Employees Records.
Maintaining Students Information
In studying Databases the following Terminologies
must be clear
This is the fact or facts about specific entity (person, place or thing).
This is the processed facts perceived to be useful by the user.
This is a single item of information or data in entity. E.g. employee
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
File Processing Systems (FPS)
Database Management systems
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).
File Processing Systems (FPS)
Information stored as groups of records in separate
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
Use of programming languages to write applications
Limitations of File Processing Systems
Separate and isolated data
Program - data interdependence
involving file formats and access
Difficulty in representing data from the
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
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
Allows for representation of data from user’s
Increases data flexibility
Superior flexibility and security over
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
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
Centralized data reduces management problems
Data redundancy and consistency are controllable
Program - data interdependency is diminished
Flexibility of data is increased
Reduction in speed of data access time
Requires special knowledge
Possible dependency of application programs to specific
A database administrator (DBA) controls and
manages the database.
Function of a DBA
Make decisions concerning the content of the
Plan storage structures and access strategies.
Provides support to users
Defines security and integrity checks
Interprets backup and recovery strategies.
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
New parent node must be created before adding a new child
Limited by rigid structure
No direct relationships between child nodes
Also has hierarchical node arrangement
But here child nodes may have more than
one parent node, or a many-to-many
The interconnected design allows for access
via multiple pathways
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
Table or Relation
Table will store information for a
Table name must be unique
The Table name should be descriptive
Column Name must be unique within
Rows must be unique
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
A duplicate value is a value in a column
of a table that exactly matches some
other values within the same column.
value in a table that may vary over time.
Most values in most tables are
You can prevent changes when it is
desirable to prevent changes in a given
column of a table
Uniquely identify each row of that table.
Every table must have only one
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
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