This document discusses databases and the relational database model. It covers key concepts like data, records, fields, and tables. It also explains entity relationship diagrams and how they are used to represent relationships between entities. Different types of relationships like one-to-one, one-to-many, and many-to-many are defined. An example entity relationship diagram is provided for a company database with employees, departments, and projects. Finally, it shows how to design tables from an entity relationship diagram by creating fields for each entity's attributes and adding foreign keys to represent relationships between tables.

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CHAPTER ONE
DATABASES
1- Data:
Data are the primary raw materials.
2-Information:
It is the output of data processing to extract the content of data or what they refer to as
indications, sign, comparisons etc.Data are the basic information
3-The table
The table is the vessel that contains a set of data of a certain topic where data are stored
4- Record:
It is the place "row" where the integrated data are stored, for example, all the
personal data of a certain person (Name, address and telephone).Etc
5- Field
The Field is the place (column), where one kind of data is stored such as the data of
(person - address ... etc).
6- Definition of Database:
Database is a group of organized data associated with a certain topic inside a table or
tables.
7-The advantages of databases
· Storing, classifying, organizing, and indexing Data in a way that can help in retrieving
them; hence they can be processed easily.
· The flexibility in modifying data through adding or exchanging data with the new ones
(Updating data).
· It is easy to create forms to make data entry easier.
· It makes search and query easy to find the stored data and information in the database.
· Displaying Data and information in form of reports in which data can be extracted ,
analyzed to support and make decision
8- Types of database in terms of (Design View):
- Hierarchical Database Model
- Network Database Model
- Relational Databases Model (They will be studied later in detail)
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CHAPTER TWO
(Entity Relationship Model)
The definition of Entity Relationship Model:
The Entity Relationship Model is one of the common styles to set an outlay for the
Relational Database that depends on the following:
1- Dividing the system to Entities such as (Employee Entity – Department Entity in a
company's system.)
2- Each Entity contains certain attributes describing and defining it (such as the
company's name, address) etc.
3- Defining the relationships among these entities and describing them as will be shown
later.
4- Represent this through a drawing, which is called:
(Entity Relationship Diagram) ERD
The importance of the Entity Relationship Diagram:
It is a prior step to implement the database in one of the programmes of the RDBMS
(Relational Data Base Management System).
It helps in making tables or files for the database and the relationships among them on
correct and scientific bases.
Entity definition:
The ' Entity' is an object that has an independent existence. It may be of a real
existence such as, an employee - a car – an item – a supplier or an abstract existence
such
as a project- a training course. Each entity has attributes that describe and define it, such
as (employee number, name, gender, address, and telephone). All these are attributes to
describe the employee Entity.
Entity Attributes Entity key
Employee Salary- address- birth date gender-name-
employee number
Employee number
Department Number of employees-location name-department
number
department number or
department name
Project location- name- project number project
Definition of the Key attribute:
It is the attribute whose value can never be recurred inside the entity.
Consequently, it distinguishes each single entity1 from the others. For example,
an employee cannot have the same national number of another.
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Secondly: Defining the relationships among the entities and their attributes:
Relationships among entities are defined in terms of …:
1- Type of relationship (One to One) or (One to Many) or (Many to Many)
Later we will explain each type.
2- The type of participation of each entity in the relationship may be either
(Total Participation or Partial Participation).
The definition of (Participation Type)
Participation means that a certain Entity depends in its existence on the necessity
of its existence in a certain relationship with another entity and in this case, it is a total
participation for this entity in this relationship. .
Example:
In the relationship of an employee in managing a department, we find that there is a
(Total Participation) for the "Department Entity". In other words, there is no department
without an employee to run. At the same time there is (Partial Participation) for
"employee entity "in this relationship, not every employee can run a department
Now we define the relationships found in the system:
(1) There are two relationships between an "Employee Entity" and
"Department Entity" they are:
a) The relationship of "work in a department" It is described as follows:
1- Each department should have a number of employees.
2- No employee can work in more than a department .
3- There is no department without employees to work in it.
4- Each employee should work in a department...
5- There are no attributes for this relationship.
Therefore:
- The relationship is ' One to Many ' between "Department Entity" and" Employee
Entity"
(1 and 2)
- There is a (Total Participation) for ' Department Entity ' in this relationship. (3)
- There is a (Total Participation) for ' Employee Entity' in this relationship. (4)
- There is no attribute for this relationship.
Summary of relationships in a company's system:
Relationship
First
The other
Relationship
Relationship
name
entity
entity
type
attributes
The entity
Total
participation
Work in a
departmen
employee department One to Many Not exist Department -
Employee
Manage a
department
employee department One to One Starting date Department
Work in a
project
employee project Many to
Many
Number of
hours
Project -
employee
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Summary for the most important used symbols in "ERD"
The meaning of the symbol symbol
Entity
Relationship
Attribute
Key attribute
The multi - valued
attribute
Derived attribute
One to One
relationship
One to Many relationship Entity
1 1 Entity a R Entity b
Entity a R Entity b
Many to Many relationship
Total participation for R the entity in the
relationship
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N
M
N 1
Entity a R Entity b
Entity a R Entity b

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CHAPTER THREE
Relational Database Model
First: Drawing a table for each entity in [ERD], we find that the fields are the attributes
of this entity:
Employee:
Employee number name gender Birth date address salary
Department
Department number Department name
Project
project number name Location
Notes:
· The name of the table is put at the top before the field name.
· One of the entity key attributes is selected to be a primary key and underline
the field name to highlight it.
· The field of (Employees number) has not been put for each "department" in
(Department Table), because the number of employees is a derived attribute.
In other words, it can be counted from the relationship between (department)
and (employee).
· Field location has not been put for the (Department table) because
(Department location) represents a multi- valued attribute. In other words, a
certain department can have more than a location as shown in the following
example; this is in case of putting the field of (Department location) in
(Department table).
Definition :
The composite key is more than a field in a table whose components together do
not recur. It distinguishes each record where as each field can be repeated solo.
1-Between the tables of (Department and Employee)
a-The relationship of "working in department ":
As the relationship "One to Many" in department table as shown in the previous
chapter from the ERD. Therefore, we will add a field in the table that represents
(Many) in the "employee table", In this case, it expresses (Department Number)
where an employee works. In other words, this field is linked to the field of
(Department number) in (Department table). In this case, it is called (Foreign Key
Field)
Definition
The Foreign Key is a strange field in a table linked to "Primary Key" in another table.
NOTE:
It is not required to nominate the foreign key with the primary field name linked
to it. However, it must be of the same type and size as shown in designing the table
using the computer.
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Definition :
The relationship of ( One to Many) between two tables means that it is possible
for a
record in the first table (One) to be linked to more than a record in the second
table
(Many ) and any record in the second table (Many) can be linked only to one
record in
the first table (One).
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