BISQL – Laymen to SQL Developer # 23 – Entity-Relationship Model #2 – ER Model Concept with an example
Hi Folks,
This post is part of Series Database Management Systems
Currently running topic for this series is listed as below :
Series of Database Management Systems
>>Chapter 1 : DBMS [Database Management Systems]
>>Chapter 2 : Database Core Concepts and Applications
>>Chapter 3 : Record Storage and Primary File Organization
>>Chapter 4 : Index Structures of Files
>>Chapter 5 : Entity-Relationship Model <You are Here>
Continuing from my previous post on this series.
We are going to Cover the Following Points in this article
- ER Model Concept with an example
ER Model Concept with an example
The basic representation of ER model is given below. After the requirement, collection and analysis phase, we create its conceptual schema step by step by using ER model concepts.
E.g.: Company database consists of
· Several departments and each department have a manager.
· Several employees work for a department.
· A department may have several locations.
· Each department controls several projects.
· We store each employee’s name, SSN, address,. An employee is assigned to one department but may work on several departments. We keep track of the number of hours per week that an employee works on each project.
· We need to keep track of employee department information for the purpose of insurance etc.
Figure The ER conceptual schema diagram for the new COMPANY database
Notations for entity relationship diagrams:
The main advantage of the ER model is its simplicity, which helps in the understanding of the overall structure of a database. An ER diagram includes the following components
![clip_image002[4]](https://sqlmentalist.files.wordpress.com/2013/07/clip_image00241.jpg "clip_image002[4]")
Figure Notations
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