Skip to main content

How to Draw An ERD For Your Database Project Tutorials

What is ERD (Entity Relationship Diagram):
ERD is stand for Entity Relationship Diagram. This is also called Logical Data Modeling.

Why we Study ERD (Entity Relationship Diagram):
Because software is an intangible thing also know as logical thing. we can't imagine it. ERD (Entity Relationship Diagram) is very helpful to understand the database design with people and designer also helpful in communications.

Components of ERD (Entity Relationship Diagram):
  1. Entity: Our object is also called an Entity. E.g; Employee., Product, Payment these are all entities.
  2. Relationships: A data Relationship is which is Exist in one or more then one Entity. E.g Employee Process Payment.
  3. Cardinality: Define the number of occurrence of the Entity. E.g; One to One, One to many , Many to Many this is a Cardinality
  4. Attributes: Attributes are Employee ID, Employee Name, Employee Address these are all attributes. There are Many types of attributes
    1. Key Attributes
    2. Derived Attributes 
Sample ERD with Attributes

Sample ERD Example

Methodology for Developing an ERD
  1. Identify Entities
  2. Find Relationships
  3. Draw Rough ERD
  4. Fill in Cardinality
  5. Define Primary Keys
  6. Draw Key Based ERD
  7. Identify Attributes
  8. Map Attributes
  9. Draw Fully Attributed ERD
  10. Check Results
We Need a case study then we implement methodology on our case study.
Case Study:
A company has several departments. Each department has a supervisor and at least one employee. Employees must be assigned to at least one, but possibly more departments. At least one employee is assigned to a project, but an employee may be on vacation and not assigned to any projects. 
  1. Identify Entities: Departments ,Supervisor ,Employee ,Project they all are Entity. 
  2. Find Relationships: Find relationship. After reading case study we make a matrix.
  3. Draw Rough ERD (Entity Relationship Diagram): Now your relation matrix is completed this is Enough information to create rough ERD. Draw a diagram and Place all the entities in rectangles . Use diamonds and lines to represent the relationships between entities.
  4. Fill In Cardinality: Identify the number of occurrences of one entity for a single occurrence of the related entity.
Here's an example drawing and the case study described above.
    • Supervisor
      • Each department has one supervisor.
    • Department
      • Each supervisor has one department. 
      • Each employee can belong to one or more departments
    • Employee
      • Each department must have one or more employees.
      • Each project must have one or more employees
    • Project
      • Each employee can have 0 or more projects.
    • Cardinality Values and symbols:
    • Rough ERD with Cardinality:

5. Define Primary Keys: Primary key is a Unique which is used to uniquely identify a specific instance.
Include the Primary keys in Rough ERD (Entity relation Diagram).


6. Draw Key-Based ERD Diagram:
  • Eliminating Many to many Relationships.
  • Adding primary key and foregin key.

we Eliminating many to many relationship in to one to one.


7. Identify Attributes:
  • data attribute is a characteristic common to all or most instances of a particular entity
  • Try to identify and name all the attributes essential to the system
  • The best way to do this is to study the forms, files and reports currently kept by the users of the system and circle each data item on the paper copy.
8. Map Attributes:

  • For each attribute we need to match it with exactly one entity. 
  • Often it seems like an attribute should go with more than one entity (e.g. Name). In this case you need to add a modifier to the attribute name to make it unique (e.g. Customer Name, Employee Name, etc.) or determine which entity an attribute "best' describes.

9. Draw Fully Attributed ERD:


10. Check ERD Result:
  • Look at your diagram from the point of view of a system owner or user. 
  • Is everything clear? 
    • Check through the Cardinality pairs. 
    • Also, look over the list of attributes associated with each entity to see if anything has been omitted.
Thanks for reading my post if you like my post then comment below. and share with your friends.




Comments

Popular posts from this blog

How to Get rid from a Facebook Virus 2015

How to Get rid from a Facebook Virus 2015: In this Article we tell you how to get rid from your Facebook virus. We tell you about Facebook virus in more details Actually when you see nude or porn posts you click on that posts this is the virus of Facebook when you click on the picture the virus is installed in your account when you login from your Desktop Computer or laptops and even mobiles this virus is automatically share with your friends or when you logout from your device that virus is automatically post on your wall and automatically tag with your all friends. Basically There are two type of viruses on Facebook. First one is automatically install on your browser cookies and when you login your profile it automatically share with all of you friends.Second one is when your click on nude pictures its automatically save on your apps. basically its an app which is share a specific kind sexual link. when you login your profile it automatically share with your friends. How to get rid f…

How To Add Breadcrumbs to Blogger

How To Add Breadcrumbs to Blogger: Breadcrumb is the navigation trail which tells about location on our site or blog to visitors. It tells readers, where (on which page) they actually are on our blog. it help to clear the structure of website to user also user can understand now where is he/she.
Breadcrumb navigation is used to create a user friendly website. Using it, readers can easily navigate to your blog by just clicking a link or few. Like in the below image, if you are on Step 3 (like: Social Media > Google Plus > Traffic) then you can easily come back to Social Media category by simply clicking on Step 1 shown on the breadcrumbs.
It also helps to increase your site’s ranking in search engines by adding keywords into your blog posts.
Adding Breadcrumb Navigation in BloggerNote: You must backup your blog template first before adding breadcrumb navigation in your blog.

Now follow below steps to Add Breadcrumb in blogger:
Go to Blogger Dashboard > Template > Edit HTMLNo…

How to Stop Auto-play Videos on Facebook

How to Stop Auto-play Videos on Facebook: In these days Facebook play their video automatically on. and it irritate which consume your internet bandwidth. if you don't want to load a video they automatically play on your screen and it take to much bandwidth. So In this Article i'll tell you how you can Stop Auto-playing Video on your timeline. Advantages of Auto-Play: When you are free and don't have any work to do then you can start browsing on Facebook. the first benefit of Auto-play is you don't need to click on play button video will playing automatically. This is the smart features of Facebook to improve the user friendly Environment for Visitors. You can watch huge collection of Videos without click on the play button and pass your time easily. Disadvantage of Auto-Play: One the The Biggest Disadvantage of Facebook Auto-Play videos consume their bandwidth if you internet package is limited then its not for you. So you can use the below tutorial to Off or Disable…