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Designing Entity Relationship Diagram (ERD)

Al Salmo Aliko .
Hello, in this post I'll discuss with you how to design good Entity Relationship Diagram ERD .
this article for:

  1. IT Students learning about database.
  2. you are having difficulties in creating ERD.
  3. you are developer that need help in database design.  
let's ask ourselves Why good database design is good ? or why we need ERD?
        when I started programming Eng / Eman Ahmed was my First teacher, she said you must write your code with pen, and now I told you good database design start with paper and pen or in technological terms start with ERD, ERD is the model which shows logical layout of your database.

let's List some advantages of good database design :
  • very low or no redundant data is stored.
  •  supporting planed or unplanned queries.
  • good design easy to maintain and modify.
  • from first glance you can understand it.
an ERD consist from Entities and relationships between them; there exist many notation in textbooks and all are right I'll use in this tutorial the most expressive and most common.

an Entity is some thing we want to store data about.
a relationship shows how entity is related to another entity.

types of relationship:
  1. One : One 
  2. One : Many
  3. Many : Many
notations :
 let's see some Examples :

see complete Example :


in the example you can see student fills Only one seat .
Student takes at least one course.
course contain at least one Student.
course is taught by Only one teacher .
teacher can Teach one or more Courses .
professor teaches zero or more sections .
section is belong to at least one course.
course has at least one section.

at the end of my post I hope you understand how Make ERD .
references:
source1  
source2

Comments

  1. UnknownJune 3, 2014 at 8:13 PM

    Thanks this info was really helpful! I used a website called Lucidchart to create my own erd diagram and it was really easy to understand. If you use diagrams often you should check it out!

    ReplyDelete
  2. UnknownJune 26, 2014 at 7:32 PM

    Thanks for the help! I have also learned How to Draw ERD (Entity Relationship Diagram) using Lucidchart and it is very user friendly and helpful! Give it a try!

    ReplyDelete

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