Ultimate Guide to ER Diagrams ( Entity Relationship Diagrams )

An Entity Relationship Diagram (ERD) is a visual representation of different data using conventions that describe how these data are related to each other. For example, the elements writer, novel, and consumer may be described using ER diagrams this way:

ER Diagram Example

ER diagram with basic objects

In the diagram, the elements inside rectangles are called entities while the items inside diamonds denote the relationships between entities. This ER diagram tutorial for beginners covers most things related to ER diagram, for quick navigation use the links below.

ER Diagrams Usage

While able to describe just about any system, ER diagrams are most often associated with complex databases that are used in software engineering and IT networks. In particular, ER diagrams are frequently used during the design stage of a development process in order to identify different system elements and their relationships with each other. For example, an inventory software used in a retail shop will have a database that monitors elements such as purchases, item, item type, item source and item price. Rendering this information through an ER diagram would be something like this:

ER diagram example with entity having attributes

ER diagram example with entity having attributes

In the diagram, the information inside the oval shapes are attributes of a particular entity.

History of ER Diagrams

ER diagrams are visual tools that are used in the Entity-Relationship model initially proposed by Peter Chen in 1976 to create a uniform convention that considers both relational database and network views. Chen envisioned the ER model as a conceptual modeling approach that views real world data as systems of entities and relationships. Entities are data objects that maintain different relationships with each other. Additionally, entities are also described further using attributes.
Since 1976, the ER model has been expanded and is sometimes used in business management, product development, and strategy formulations. However, database design remains its primary application.

ER Diagram Symbols and Notations

Elements found in ER diagrams

Elements in ER diagrams

There are three basic elements in an ER Diagram: entity, attribute, relationship. There are more elements which are based on the main elements. They are weak entity, multivalued attribute, derived attribute, weak relationship and recursive relationship. Cardinality and ordinality are two other notations used in ER diagrams to further define relationships.

Entity

An entity can be a person, place, event, or object that is relevant to a given system. For example, a school system may include students, teachers, major courses, subjects, fees, and other items. Entities are represented in ER diagrams by a rectangle and named using singular nouns.

Weak Entity

A weak entity is an entity that depends on the existence of another entity. In more technical terms it can defined as an entity that cannot be identified by its own attributes. It uses a foreign key combined with its attributed to form the primary key. An entity like order item is  a good example for this. The order item will be meaningless without an order so it depends on the existence of order.

Weak Entity in Entity Relationship Diagrams

Weak Entity Example in ER diagrams

Attribute

An attribute is a property, trait, or characteristic of an entity, relationship, or another attribute. For example, the attribute Inventory Item Name is an attribute of the entity Inventory Item. An entity can have as many attributes as necessary. Meanwhile, attributes can also have their own specific attributes. For example, the attribute “customer address” can have the attributes number, street, city, and state. These are called composite attributes. Note that some top level ER diagrams do not show attributes for the sake of simplicity. In those that do, however, attributes are represented by oval shapes.

Attributes in ER Diagrams

Attributes in ER diagrams, note that an attribute can have its own attributes ( composite attribute )

Multivalued Attribute

If an attribute can have more than one value it is called an multivalued attribute. It is important to note that this is different to an attribute having its own attributes. For example a teacher entity can have multiple subject values.

Multivalued attribute in entity relationship diagrams

Example of a multivalued attribute

Derived Attribute

An attribute based on another attribute. This is found rarely in ER diagrams. For example for a circle the area can be derived from the radius.

Derived Attribute in ER diagrams

Derived Attribute in ER diagrams

Relationship

A relationship describes how entities interact. For example, the entity “carpenter” may be related to the entity “table” by the relationship “builds” or “makes”. Relationships are represented by diamond shapes and are labeled using verbs.

Relationships in ER diagrams

Using Relationships in Entity Relationship Diagrams

Recursive Relationship

If the same entity participates more than once in a relationship it is known as a recursive relationship. In the below example an employee can be a supervisor and be supervised, so there is a recursive relationship.

Recursive Relationship in ER Diagrams

Example of a recursive relationship in ER diagrams

Cardinality and Ordinality

These two further defines relationships between entities by placing the relationship in the context of numbers. In an email system, for example, one account can have multiple contacts. The relationship in this case follows a “one to many” model. There are number of notations used to present cardinality in ER diagrams. Chen, UML, Crow’s foot, Bachman are some of the popular notations. Creately supports Chen, UML and Crow’s foot notations.The following example uses UML to show cardinality.

Cardinality in ER diagrams

Cardinality in ER diagrams using UML notation

Tips on How to Draw ER Diagrams

Because ER diagrams are simple enough to understand, just about anyone can create them. However, two different ER diagrams describing the same system may still be radically different in terms of their simplicity, completeness, and efficiency at communicating the system. In other words, there are good ER diagrams and there are poor ones.

Because this ER tutorial focuses on beginners below are some tips that will help you build effective ER diagrams:

  1. Identify all the relevant entities in a given system and determine the relationships among these entities.
  2. An entity should appear only once in a particular diagram.
  3. Provide a precise and appropriate name for each entity, attribute, and relationship in the diagram. Terms that are simple and familiar always beats vague, technical-sounding words. In naming entities, remember to use singular nouns. However, adjectives may be used to distinguish entities belonging to the same class (part-time employee and full time employee, for example). Meanwhile attribute names must be meaningful, unique, system-independent, and easily understandable.
  4. Remove vague, redundant or unnecessary relationships between entities.
  5. Never connect a relationship to another relationship.
  6. Make effective use of colors. You can use colors to classify similar entities or to highlight key areas in your diagrams.

You can draw entity relationship diagrams manually, especially when you are just informally showing simple systems to your peers. However, for more complex systems and for external audiences, you need diagramming software such as Creately’s to craft visually engaging and precise ER diagrams. The ER diagram software offered by Creately as an online service is pretty easy to use and is a lot more affordable than purchasing licensed software. It is also perfectly suited for development teams because of its strong support for collaboration.

ER Diagram Templates

Below are some ER diagram templates so you can get started quickly. Clicking on the image and in the new page that opens click the “Use as Template” button. For more templates check out ER diagram templates article.

ER Diagram Template

ER Diagram Template of exam database ( Click on the image to use as template )

A basic ER diagram template for a quick start

Entity Relationship Diagram Template

Basic ER Diagram template ( Click to use as template )

Benefits of ER diagrams

ER diagrams constitute a very useful framework for creating and manipulating databases. First, ER diagrams are easy to understand and do not require a person to undergo extensive training to be able to work with it efficiently and accurately. This means that designers can use ER diagrams to easily communicate with developers, customers, and end users, regardless of their IT proficiency. Second, ER diagrams are readily translatable into relational tables which can be used to quickly build databases. In addition, ER diagrams can directly be used by database developers as the blueprint for implementing data in specific software applications. Lastly, ER diagrams may be applied in other contexts such as describing the different relationships and operations within an organization.

References

1. Entity-relationship model as published on Wikipedia.
2. Entity Relationship Diagram by Mike Chapple as published on the About.com website
3. Entity-Relationship Modelling by Craig Borysowich as published on the Toolbox.com website

Author

Nishadha

Software engineer turned tech evangelist. I handle marketing stuff here at Creately including writing blog posts and handling social media accounts. In my spare time I love to read and travel. Check out my personal blog Rumbling Lankan where I write about online marketing stuff.

Comments

  1. tanvir

    best sites for erd diagram. can any one tell me the date of the artical posted??

  2. MalcolmT

    The model that you espouse (attributes in ovoids, aka ‘the lollipop model’) is OK for small systems with very limited number of attributes per entity. Unfortunately, some students try to use it for llarger assignments (20 entities with up to 20 attributes per entity) and the whole model becomes unreadable unless they use A2-sized paper. If I never see another model of this type, it will too soon!!

  3. A very good explanation for ER diagrams.

  4. Pradeep Alahakoon

    Information in this site are very usefull.tankx v m.

  5. Ankit Doshi

    I am an Engineering Student and needed this for my exams.
    I can now surely bet on it that I can crack any ER-Diagram
    Thanks to author.

  6. maina

    i need a ISA relationship with some example

  7. minie

    Jus wrote my Database exam, wish id seen this much earlier.

  8. Naresh

    Ya its very good explanation about ER-Diagrams

  9. Angel

    very nice simple and attractive explanations.

  10. utpal swain

    i cleared much of my concept and doubts…….thanks

  11. ratul

    thanx a Lot….

  12. gopika

    this is very useful for us. so easy to understand.

  13. Ashish Garg

    Its interesting… Nice presentation…. Thnx

  14. Vik

    Very to the point and clear explanation. Good read to refresh the concepts just in few minutes. Thanks.

  15. Aseem

    A lucid and elaborate explanation. Appreciable.

  16. suman

    gud explanation…

  17. sheha

    Thank u ,this was very big help for us….

  18. asad

    best example of ERD

  19. benzie

    A very clear explanation of ERD with the aid of diagrams.thanx.

  20. benzie

    superb examples of ERD

  21. Giedre

    Hi, I have to do an ER model for a travel game app but we have not been shown how in college. Can anyone please give me some ideas on how to go about this.

    The player or multiple players are required to navigate their way to the objective location using the transport infrastructure in a city or area, the games A.I places them in. The maps will be updated on a frequent basis to add variety to the user’s experience.

    Thanks

  22. M.RAMAR

    i want a relationship between er diagram and uml diagram

  23. kavi

    vry clear explanation

  24. nikhil

    cleared my most of the doubts , thank you 😀

  25. Thanks for sharing , it is very useful for database designing.

  26. Aditya Bhowmick

    Thank you sir ,I don’t know how to create a ERD, but now I clear this.

  27. Sofyan Gustaf

    Very useful
    Explanation is very clear

  28. prasanna

    actually,this is good stuff…thanks lots…

  29. THIS IS VERY RELEVANT FOR MY SAAD PAPER EXAM

  30. thanks a lot..nicely written…

  31. Qaiser

    the best website..!

  32. Inder

    Draw ER diagram for the following “A
    teacher can teach many courses. A student
    can enrol in many courses. A course may
    be a part of one or many programmes. A
    teacher can be mentor of many students,
    however a student can have only one
    mentor.”

    Can you answer above Q Please

    • Dart Vader

      Inder, I know I’m replying quite late, but tell me if the correct answer is what I thought: to put every relation as 1..n, with one exception: the teacher/student relation. Here I put 1 in the Teacher side and 1..n in the student’s side. Is it correct? Thanks!

  33. nishath

    Examples are very simple and useful to understand ER Diagram.But if you take a simpl eproblem statement and explain how to identify entity,relationships etc… it would be more helpful to understand.

  34. Tushar

    what exactly connector image in entity relationship diagram????

  35. brunswick

    hey, brow.. nice job.. thanks for this.. it gave us so much help.. thanks brow..

  36. MULUKEN ASHAGRIE

    I HAVE GOTE A GOOD HELP.THANK U!

  37. TAPAS

    thanks,very good explanation for all.

  38. Rudresh DN

    Its really good. Understanding the basic concepts of ER diagram with simple language with very good examples. It is easy to for us to know the contents. Thank You Sir.

  39. dinesh92

    i have some five problem like this can u help?
    1.Cargo Tracking Management System
    2.Supermarket Sales and Inventory Control System
    3.Emergency Call Management System
    4.Job Management System

    I want to what are the entities of these problems?

  40. kandyjet

    very nice explanation. Thank you for the time.

  41. Latyfa

    Simple, clear, easy.
    Thank you so much, that was really helpful.

  42. Lahiur

    Thanks…..really good for beginners. it is very good if you can add some solved question regarding ER diagrams….. :)

    • Nishadha

      Hi Lahiur,
      We’ll try to add some example questions in the future.

  43. Sachin

    I have still confusion on creating a relationship between two entities,does relationship block have also attributes of its own please help me with this.

  44. Nishadha

    Hi Sachin,
    Relationships can have their own attributes as well.

  45. parkash

    Nice…… thank u………..

  46. simply superb n easy…..
    thank u….

  47. thanks dude very usefull for me…….

  48. ammar

    nice,and very helpful for our subejct in database management system……….

  49. Tharindu

    Good Learning Web Site

  50. ASHISH KUMAR

    its an amazing ans ,and i am so satisfied with this ans

  51. AK

    I was just wondering…I have an application form with me…the link is attached below. Could you please tell me what entities exist within this application form?
    For instance, one entity would be applicant—> attributes consisting of Fname, Lname, address…etc

    Your help would be greatly appreciated.

    Application form:
    http://dairyqueenwest.com/employmentapplication.pdf

  52. ALEX O.

    you’re a genius,i cherished you.

  53. Eugene Alza

    Its soo hard and I am thinking deeply in my project Callisto Groceru Store. I dont know what is the flow of this grocery store

  54. Zahida Laghari

    nicelly defined , i want to make ER diagram for press club. I have some confusions but
    after visit this website i have believe Insha Allah i will make easilly.

  55. Mutahir NAseer

    Very Nice Answer and m really satisfied from it and also my concept is clear from it .

  56. Cool post! :)
    Check out my blog too :)

  57. Shaik Imran

    nice… Insha allah it may help me in designing ERD for my project…

  58. Taukir Ahamd

    best defination and example

  59. sekate mubaraka

    exact requests have been provided best arrangement of databases

  60. deepak

    Thanks. My concept is clear from it.

  61. draherbal

    with a diagram can be seen apparently from one component to the other components of related this way will be easier for people to understand the meaning

  62. thyagaraj

    Im new to dbms….i got help from ur article,,,,thanku so much

  63. Rajiv

    Thanks for such a nice explanation\

  64. Sandeep Patel

    hello
    what we can show relationship of PK and FK using ER Diagram..???

  65. Rohan Nagpal

    I required this for my dbms exam in the morning. This article is so well explained enough for a one legged man to run a marathon. Thank you dear editor.

  66. getinet

    add more related examle but the other thing is good i think

  67. radhika

    good description for ER diagrams…

  68. Zaharaddeen Elhassan

    thanks , excellent explanation, simple English and easy to understand

  69. suthakaran gobal

    Best explanation for beginners !

  70. Nupur

    CooooOl.. TotAlLy RoCKs’..

  71. pavi

    this is very useful for the students :-)

  72. Chow

    Very clearly explained :)

  73. Sijovw

    Thanks dear. but i also need to know about the ‘arrow headed line’ and ‘double lines’ . Can we use arrow heads in ER diagrams? If it is, then how?

  74. Prashant

    You can add relationship sets between two entities after you are done making entity sets right ?

  75. asghar khan

    thanxs…very simple and easy to understand….

  76. ANAND

    its very good n very easy to understand

  77. Frances

    Thank you so much. Your explanation made my module easy for me :)

  78. good explaination and its very useful
    thanx

  79. Virtue

    the most good and easy to understand explanation,thank you….

  80. saroj dongol

    Great Tutorial… Love it

  81. DANCAN

    very very nice article. really helped me out.. . .

  82. Jaison

    good .u can also draw the attributes from the entity tablle as a little ballon , on top of the ballon u can write the entity names.

  83. shereenzaman

    Good example of ERD

  84. ritu jain

    we cannot get a proper charts so elaborate these site more

  85. raphael lenarisiolo

    Good explanation for ER-Diagrams,it really helped me in my examination.

  86. Hosein

    Hi
    I want draw a ERD of website news?

  87. I am impressed how easily he described erd and relatons easily..god bless you

  88. Haroon

    It is good to understand!

  89. Jamal

    What about the tables in a database which are not interrelated? How to show ER diagram of a complete database with few related tables and few other non-related tables. It’s not necessary that each and every table in a database in interrelated.

  90. anony

    really helpfull thanks! :-)

  91. Neha

    Can someone please explain all the notations used in er diagram?

  92. Swapnil

    Very descriptive and useful article. Helped me for my SE project.

  93. jessy

    thank you so much for the information…

  94. Isuru Prasad

    Dear sir thank you for this. today is my exam. i did not knw anything about ER diagram. i guess i can write nicely for exam to. thank u again

  95. prakash

    Thank you so much sir.. Its very usefull for me…

  96. Nana parkhe

    The author explained the ER model in a simple & understandable language.

  97. RAM GITE

    VERY NICE THIS EXPLAINATION , I LIKE ITS SIMPLE SOLUTION THANK U …………..

  98. leila

    thank you…verry well…leila from iran

  99. pakistani

    bhenchod indian kutte da puttar

  100. sejal khunt

    hi i am student of b.c.a 6th sem. ,i can’t draw ER diagram for my project website.in my project i have 4 database tables so, how i creat ER diagram

  101. usha

    A Supplier located in only one city supplies various parts for the project to different companies located in various cities. Draw the “E-R” for the supplier and parts database.

    can i get the ER diagram for this

  102. Abraham Dinakaran

    Good . I need learning materials on UML stuffs for handling and guiding projects for students

  103. tkmd

    i am a teacher trainee of ict thank you v,much

  104. Haritha

    Many readers will be benefiting from your blog. Thanks for listing the ERP Diagrams which is necessary software for businesses. Thanks for sharing such a useful diagrams list..

  105. musa

    thanks a lot Nishada, I benefited a lot from your staff. May God reachly bless you. Amen

  106. zulekha khan

    Well explained…. So help full….

  107. shayankhan

    here we gain lots of info thank dude by making this such type of articles ……really appreciated

  108. Amritpal

    Awesome guide for ERD, i understand a lot of about creating a good erds in half hour.

    appreciated from heart.

  109. Gagan

    Thank you sooo much for this blog. It really helps me a lot to create ER Diagram for my project. Well Explained :)

  110. It is really ultimate explanation. Thanks to creately.com team.

  111. Mustafa

    Good definition,that a ER diagram may has.

  112. Dimitar

    A gud tut…..big up……From Kenya

  113. khilji

    if this is ERD then what will be DFD
    just check r u talking about ERD or DFD

  114. Umair

    exellent explanation for ER diagram……….

  115. vlc

    Never seen this notation before… everything looks like 1:1 … mixes attribute relations, entity relations, and verbs. Anyway.. at least it is a notation.

  116. Samarjeet

    Great learning. Keep up the good work

  117. Sheela

    Thanks for the post. Very good explanation. Good color highlights to explain the diagrams.

  118. Dzinaishe

    Best explanation of E R Diagrams i have met so far. Good job Nishada

  119. sushma

    A unique blog as your name … Very simple and easy.. relevant examples !! keep up the good work …..

  120. Faizal

    Thanks sir for your share. alhamdulillah ur explaination just simple n great. A week on understanding the lecturer but still blur,juz read your in 5 min the thing be cleared

  121. Deepika

    very nice!!!! esay to understand.Really nice article.Thanks!!!! keep doing this it will be very helpfull…..

  122. Asvitha

    Got satisfied with what is needed.Thank you.

  123. Angela Vaughn

    This was a great explanation of ERD. I’m currently taking a class a database concepts class at University of Phoenix. The details describe here was clear, and will help me with my assignments. Thank you! :-)

  124. Priyanka

    It’s Really Useful thank you..

  125. sudhansu

    *********very nice *********thank you***********

  126. Ali Ahmadi

    Very very Nice tutorial Thank you Very Much.
    I’d a Question: Which kind of Attribute is the Date?

  127. Amad

    Really very nice & helpful article. this is really nice diagrams tutorial you did good job Thank you

  128. aaravi

    sir, i don’t know how to create er-diagram for inventory management system so pls you give me to create er-diagram for inventory management system.
    i made database tables but i don’t know how to create er-diagram.
    pls quick reply.
    plsssssssssssss sir quick create er-diagram

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