So you want to learn Entity Relationship diagrams? This ER diagram tutorial will cover their usage, history, symbols, notations and how to use our ER diagram software to draw them. We’ve also added some templates for you to get started quickly.
What is an ER diagram?
An Entity Relationship Diagram (ERD) is a visual representation of different entities within a system and how they relate to each other. For example, the elements writer, novel, and a consumer may be described using ER diagrams the following way:
History of ER Diagrams
Although data modeling has become a necessity around 1970’s there was no standard way to model databases or business processes. Although many solutions were proposed and discussed none were widely adopted.
Peter Chen is credited with introducing the widely adopted ER model in his paper “The Entity Relationship Model-Toward a Unified View of Data“. The focus was on entities and relationships and he introduced a diagramming representation for database design as well.
His model was inspired by the data structure diagrams introduced by Charles Bachman. One of the early forms of ER diagrams, Bachman diagrams are named after him.
For a detailed history of ER diagrams and the evaluation of data modeling, refer this article.
What is the use of ER Diagrams?
What are the uses of ER diagrams? Where are they used? Although they can be used to model almost any system they are primarily used in the following areas.
ER Models in Database Design
They are widely used to design relational databases. The entities in the ER schema become tables, attributes and converted the database schema. Since they can be used to visualize database tables and their relationships it’s commonly used for database troubleshooting as well.
Entity relationship diagrams in software engineering
Entity relationship diagrams are used in software engineering during the planning stages of the software project. They help to identify different system elements and their relationships with each other. It is often used as the basis for data flow diagrams or DFD’s as they are commonly known.
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:
In the diagram, the information inside the oval shapes are attributes of a particular entity.
Entity Relationship Diagram (ERD) Symbols and Notations
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, multi valued 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 be 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 the order.
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.
Multivalued Attribute
If an attribute can have more than one value it is called a multi-valued attribute. It is important to note that this is different from an attribute having its own attributes. For example, a teacher entity can have multiple subject values.
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.
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.
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.
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 a 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.
How to Draw ER Diagrams
Below points show how to go about creating an ER diagram.
- Identify all the entities in the system. An entity should appear only once in a particular diagram. Create rectangles for all entities and name them properly.
- Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship.
- Add attributes for entities. Give meaningful attribute names so they can be understood easily.
Sounds simple right? In a complex system, it can be a nightmare to identify relationships. This is something you’ll perfect only with practice.
ER Diagram Best Practices
- 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.
- Remove vague, redundant or unnecessary relationships between entities.
- Never connect a relationship to another relationship.
- Make effective use of colors. You can use colors to classify similar entities or to highlight key areas in your diagrams.
Drawing ER Diagrams Using Creately
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 our ER diagram templates section.
A basic ER diagram template for a quick start
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.
Feedback on ER Diagram Tutorial
I’ve done my best to cover all you need to know about ER diagrams. If you think I’ve missed some part make sure to mention that in the comments sections. It’s a good place to ask questions too.
References
1. Entity-relationship model as published on Wikipedia.
2. Entity Relationship Diagram by Mike Chapple as published on the About.com website
Nice lesson. I appreciate your help.
i want to know the rules of aggregation, specialization and generalization
Very nice detailed description except for the cardinality part. If that can also be elaborated a little, then it can be the best place to learn ERDs.
If I have big er diagram which can not plot in one page what should I have to do??
Hi Niraj, when publishing large diagrams, you can use the Creately viewer to do so. You can get the diagram embed code via the Publish tab. For more information refer https://creately.com/blog/creately/the-new-creately-viewer/
this explanation is very good and fairly easy to understand. I might have to review Cardinality and Ordinality once or twice more but the rest was very concise and clear. Thank you.
Indeed best explanation
it is very important to me…….tnx
Hi Nishadha,
Explanation is so good and easily understandable. I have some doubts. I’ve taken a DBMS-1 course in my Master’s and my professor taught me ERD differently. For relationships he used triangle, not a diamond. In cardinality he didn’t use UML, Chen or Crow’s foot notations. He used some thing different, like Thick lines, thin lines, one-sided arrows etc. Could you help me to figure out what notations are those and also I am curious enough to know which notation is used widely. Please help me with this.
Thanks.
Nice explanation….simple and understandable
Yusuph Khamis Pius from TANZANIA
Thank you. This is understandable!
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Very very Nice tutorial Thank you Very Much.
I’d a Question: Which kind of Attribute is the Date?
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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! 🙂
Got satisfied with what is needed.Thank you.
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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
A unique blog as your name … Very simple and easy.. relevant examples !! keep up the good work …..
Best explanation of E R Diagrams i have met so far. Good job Nishada
Thanks Dzinaishe. Glad you like it. Feel free to tweet and share it across social networks.
Thanks for the post. Very good explanation. Good color highlights to explain the diagrams.
Thanks Sheela, Glad you enjoyed it.
Great learning. Keep up the good work
Never seen this notation before… everything looks like 1:1 … mixes attribute relations, entity relations, and verbs. Anyway.. at least it is a notation.
exellent explanation for ER diagram……….
if this is ERD then what will be DFD
just check r u talking about ERD or DFD
A gud tut…..big up……From Kenya
Good definition,that a ER diagram may has.
It is really ultimate explanation. Thanks to creately.com team.
Thank you sooo much for this blog. It really helps me a lot to create ER Diagram for my project. Well Explained 🙂
Awesome guide for ERD, i understand a lot of about creating a good erds in half hour.
appreciated from heart.
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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..
i am a teacher trainee of ict thank you v,much
Good . I need learning materials on UML stuffs for handling and guiding projects for students
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
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
bhenchod indian kutte da puttar
thank you…verry well…leila from iran
VERY NICE THIS EXPLAINATION , I LIKE ITS SIMPLE SOLUTION THANK U …………..
The author explained the ER model in a simple & understandable language.
Thank you so much sir.. Its very usefull for me…
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
thank you so much for the information…
Very descriptive and useful article. Helped me for my SE project.
Can someone please explain all the notations used in er diagram?
really helpfull thanks! 🙂
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.
It is good to understand!
I am impressed how easily he described erd and relatons easily..god bless you
Hi
I want draw a ERD of website news?
Good explanation for ER-Diagrams,it really helped me in my examination.
we cannot get a proper charts so elaborate these site more
Good example of ERD
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.
very very nice article. really helped me out.. . .
Great Tutorial… Love it
the most good and easy to understand explanation,thank you….
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thanx
Thank you so much. Your explanation made my module easy for me 🙂
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thanxs…very simple and easy to understand….
You can add relationship sets between two entities after you are done making entity sets right ?
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?
Very clearly explained 🙂
this is very useful for the students 🙂
CooooOl.. TotAlLy RoCKs’..
Best explanation for beginners !
thanks , excellent explanation, simple English and easy to understand
good description for ER diagrams…
add more related examle but the other thing is good i think
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.
hello
what we can show relationship of PK and FK using ER Diagram..???
Thanks for such a nice explanation\
Im new to dbms….i got help from ur article,,,,thanku so much
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
Thanks. My concept is clear from it.
exact requests have been provided best arrangement of databases
best defination and example
nice… Insha allah it may help me in designing ERD for my project…
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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.
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
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Good Learning Web Site
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Nice…… thank u………..
Hi Sachin,
Relationships can have their own attributes as well.
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.
Thanks…..really good for beginners. it is very good if you can add some solved question regarding ER diagrams….. 🙂
Hi Lahiur,
We’ll try to add some example questions in the future.
Simple, clear, easy.
Thank you so much, that was really helpful.
very nice explanation. Thank you for the time.
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?
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.
thanks,very good explanation for all.
I HAVE GOTE A GOOD HELP.THANK U!
hey, brow.. nice job.. thanks for this.. it gave us so much help.. thanks brow..
what exactly connector image in entity relationship diagram????
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.
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
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!
we have teacher , students,course ,programmes as entities . first of all, the relationship among teacher and courses are (teach) and it should be many to one due a teacher can teach many course but the course should take by one teacher. the second relationship between student and course is (Enrol in) beacuse and it should be one to many. the third relationship is course and programmes . im so tired hhhhhhh to write buishut
the best website..!
thanks a lot..nicely written…
THIS IS VERY RELEVANT FOR MY SAAD PAPER EXAM
actually,this is good stuff…thanks lots…
Very useful
Explanation is very clear
Thank you sir ,I don’t know how to create a ERD, but now I clear this.
Thanks for sharing , it is very useful for database designing.
cleared my most of the doubts , thank you 😀
vry clear explanation
i want a relationship between er diagram and uml diagram
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
superb examples of ERD
A very clear explanation of ERD with the aid of diagrams.thanx.
best example of ERD
Thank u ,this was very big help for us….
gud explanation…
A lucid and elaborate explanation. Appreciable.
Very to the point and clear explanation. Good read to refresh the concepts just in few minutes. Thanks.
Its interesting… Nice presentation…. Thnx
this is very useful for us. so easy to understand.
thanx a Lot….
i cleared much of my concept and doubts…….thanks
very nice simple and attractive explanations.
Ya its very good explanation about ER-Diagrams
Jus wrote my Database exam, wish id seen this much earlier.
i need a ISA relationship with some example
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.
i need help for er diagram if you will
Information in this site are very usefull.tankx v m.
A very good explanation for ER diagrams.
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!!
best sites for erd diagram. can any one tell me the date of the artical posted??