Entity- relationship model

 Topic Outline


Entity-relationship model
Elements of Entity-relationship model

  • Entities
  • Attributes
  • Relationship


Entity-relationship model

The entity-relationship model was introduced by Peter Chen in 1976. ER model is a logical representation of data in an organization. The entity-relationship model is used to describe the elements of a system and their relationships. 

Elements of  Entity-relationship model

The element of the entity-relationship model is as follows:


1: Entities

The entity is a person, place, object, thing, or event for which data is collected and maintained in a database. The entity is represented by a rectangle. The name of the entity is written inside the rectangle. 

Text Box

For example

A library system may contain data about different entities such as BOOK, Member, NAME, DEPARTMENT ETC. A university system may include entities such as STUDENT, TEACHER, DEPARTMENT, CLASS, ROLL NO, etc. 

Examples of entities are as follows:

Place: CITY, PROVINCE, COUNTRY

Person: STUDENT, DOCTOR, TEACHER, PLAYER, PATIENT, ENGINEER

Object: PENCIL, TOY, VEHICLE, EQUIPMENT

Event: ADMISSION, BUY, SELL, REGISTRATION

Concept: ACCOUNT

The entity is used in different meanings that are below:

  • Entity Type

The entity with the same attributes is called entity type. All entities share common characteristics. For example, the DEPARTMENT entity type is a collection of all departments and the TEACHER entity type is a collection of all teachers, etc.

  •  Entity Instance

The member of an entity class is also known as entity instance. Each entity instance of an entity type has its own value. For example, a TEACHER Abdullah of TEACHER entity type is an entity instance.

  • Entity Set

 A set of all entities of a specific entity type in the database is called an entity set. For example, the entity set TEACHER may consist of all teachers in the university. The entity set PATIENT may consist of all patients in the hospital. 

  • Types of Entities

    • Weak Entity

A weak entity is an entity that exists if another entity exists. A weak entity depends upon the existence of another entity. 

    • Strong Entity

A strong entity is an entity that exists without depending upon the existence of another entity.

    • Associative Entity

It associates the instances of one or many entity types with one another. The attributes of an associative entity represent the relationship between the entity instances.

2: Attributes

The characteristics of an entity are called attributes. For example, the Name, Address, Phone no, Email of a teacher are his attributes. All instances of a specific entity class have the same attributes. For example, all teachers of the TEACHER entity class have the attributes of Name, Address, Phone no, and Email.

  • Attribute Domain

It is a set of possible values for an entity. All attributes have a domain. A domain consists of a range of values or discrete values. For example, the domain for Gender attributes can be Male or Female. 

  • Types of Attributes

Different types of attributes are as follows:

    • Simple Attribute

Attribute that can not be subdivided into a component is called simple attribute. A simple attribute is also called an atomic attribute. For example, a person can have only one gender.


Shape   

    • Composite Attribute 

An Attribute that can be subdivided into smaller components is called a composite attribute. For example, Address is a composite attribute because it can be divided into Country, Street, House no, City.

 

    • Single-Valued Attribute

An attribute that contains only one value is called a single-valued attribute. For example, the Gender of a person is a single-valued attribute.

    • Multi-Valued Attribute

An attribute that contains more values is called a multi-valued attribute. The multi-valued attribute is represented by a double line oval. For example, a person can have two or more phone numbers. Similarly, a student may have different skills. 


 

    • Stored Attribute

An attribute stored in a database is called a stored attribute. These attributes are accessed from a database.

3: Relationships 

A relationship is a logical connection between entities. Entities that participate in a relationship are called participants. A relationship may exist between different entities or between an entity and itself. For example, a relationship exists between a TEACHER and STUDENT because the teacher teaches the student.

  • Total relationship

If all entities of that entity set may be a participant in the relationship, this relationship is called a total relationship.

  • Partial relationship

If some entities of that entity set may be a participant in the relationship so, this is called a partial relationship.




Comments

Post a Comment

If you have any doubts, please let me know

Popular Posts

Computer Abbreviation

Topic Outline Introduction to computer abbreviation Abbreviation of system unit component  Abbreviation of storage devices  Abbreviation of input and output devices  Abbreviation of data communication and computer network Abbreviation of Programming Languages Abbreviation of Operating System and Networks  In this lecture, we will discuss the different Computer Abbreviations. Introduction to Computer & Information technology   Abbreviation   Full-Form   1   Computer     Common Operating Machine Particularly Used for Technological and Education Research   2   IPC   Information Processing Cycle   3   IT   Information Technology   4   PC   Personal Computer   5   CPU   Central Processing Unit   6   USB   Universal Serial Bus   7   ENIAC   Electronical Numerical Integrator and Calculator   8   EDVAC   Electronic Discrete Variable Autom...
Read more

Transport Layer

Image
  Topic Outline Transport Layer TCP Function of TCP UDP Difference between TCP and UDP Transport Layer The Transport layer is essentially responsible for delivering data to the appropriate application on the host computer. It receives requests from the application layer protocols and passes them down to the internet network layer. Two most commonly used transport layer protocols are the connection TCP and connection UDP. TCP  Transmission Control Protocol End to End communication for user processes. Processes can communicate in a simple stream of binary data. Each byte of data will arrive in the order it was sent. If some part of the data cannot be received this will be made explicit by an error being passed to the user code. Functions of TCP   (1) Data Transfer TCP transfer a continuous stream of bytes. TCP itself decides how to segment the data and it may forward the data at its own convenience. (2) Reliability TCP assigns a sequence number to each byte transmitted and ...
Read more

Introduction to Database

 Topic Outline Introduction to Database  Types of Data Metadata Components of Database Environment Application Program Range of Database applications Types of Users Types of Data Different types of data are as follow: Numeric Data It consists of numeric digits from 0 to 9 like 22, 58, 1123, or -123. The numeric data may be, either positive or negative. Alphabetic Data It consists of alphabetic letters from A to Z, a to z, and blank spaces. For example, "Computer", "Software", "IT", and "Automata" etc. Image Data Image data includes graphs, pictures, drawings,, and charts. Image data is more comprehensive.  Alphanumeric Data It consists of numeric digits (0 to 9) , letters (A- to Z) and all special characters (+, -, @, $, #) etc. Audio Data This data includes music, speech, and any type of sound. Video Data This data is a set of full-motion images played at a high speed. It is used to display actions and movement. Metadata The metadata can be defi...
Read more

Types of database

Topic Outline Types of Database Object-Oriented Database Centralized Database Decentralized Database Distributed Database Hierarchical Database Personal Database Cloud Database Multi-Dimensional Database Operational Database Relational Database  1:Object-Oriented Database Object-oriented database stores data in the form of objects. An object is an item that can contain data and functions. For example, an object employee may contain data about an employee such as Employee ID, Name, Address, Phone Number, etc. It may also contain functions to process the data such as printing the record of an employee, calculating salary, etc. Characteristics The object-oriented data model must be able to provide complex object representation. The object-oriented data model must be extensible. It means it provides support for defining new data types and methods. The object-oriented data model must support encapsulation or information hiding. The object-oriented data model must exhibit inheritance. In...
Read more

Threads in operating system

Image
  Topic Outline Threads Difference between thread and process Types of Threads Kernel Level Thread User Level Thread Multithreading Advantages Resource Sharing Responsiveness Utilization of Multiprocessor Architecture Multithreading Models Many to One Model One to One Model Many to Many Model Threads Thread is a basic unit of CPU utilization. Thread is also called a lightweight process. Thread is a process within a process but it does not have its own process control block. In a process, multiple threads are created. In a process, multiple threads allow multiple executions.   The thread consists of the following things. Thread ID Register Program counter Stack Difference between threads and process. Threads   Process   In threads no system  call  is  involved .   In a process system call is  involved .   Thread  is  a  lightweight  process.   The Process is  heavyweight .  If  the th...
Read more

Display devices

Image
  Topic Outline Display devices Types Cathode Ray Tube Flat Panel Display Emissive Display LED OLED Gas Plasma Non-Emissive Display LCD A display device is an output device. It is used to represent information in the form of text, graphics, images, and video. The display for a desktop computer is a monitor. Mobile computers and devices integrate the display in the same physical case. Some displays have touch screens such as mobile phones and laptops etc. The output displayed by a display device is called soft copy. Display devices are available in different sizes. For example When we write any document on the computer, it is a soft copy of the document. When we get a print of this document, it is a hard copy of the document. Types Types of display devices are as follows. (1) Cathode Ray Tube A cathode-ray tube creates an image on the screen by using a beam of electrons. Cathode ray tube consists of one or more guns. These guns fire a beam of electrons inside the screen. The monitor...
Read more

Shortcut keys of computer

Important Shortcut keys of Computer Shortcut keys are an easier and quicker method of executing the commands in the computer system. When we work on the computer, different shortcut keys are used. Some important shortcut keys are as follow: Short cut keys   Working   Ctrl+ C   Copy the select item   Ctrl+ V   Paste the item   Ctrl+ X   Cut the select item   Ctrl+ Del   Cut the select item   Ctrl+ A   Select all text   Ctrl+ Home   Go to beginning of the document   Ctrl+ End   Go to end of the document   Ctrl +( left arrow)   Move one word to the left at a time   Ctrl +( right arrow)   Move one word to the right at a time   Ctrl +( Plus key)   Adjusts width in window explorer   Ctrl +( Minus key)   Adjust width in window explorer   Ctrl+ Alt+ Del   Windows task manager   Ctrl+ Ecs   Bring up the start menu   Ctrl+F4   Close window in progra...
Read more

History of Computer

Image
  Topic Outline History of computer Abacus John Napier's Bone Blaise Pascal Von Leibnitz Charles Xavier Joseph Charles Babbage Herman Hollerith Atanasoff George Boole Mark 1 Computer ENIAC  EDVAC UNIVAC Commercial Computer History of computer Today those computers that we are used behind this many efforts of different peoples. An Abacus computing device was used for addition and subtraction. John Napier Bones created the slide rule to perform mathematical calculations. Blaise Pascal invented the mechanical machine for adding and subtracting. Von Leibnitz also invented the calculating machine that was used for division and multiplication. Charles Xavier invented the machine that could perform addition, subtraction, multiplication, and division.  Charles Babbage invented a difference engine and an analytical engine. A brief history is available below👇. The computer was invented because 'necessity is the mother of invention'. A brief history behind the invention of the comp...
Read more