What is Entity Relationship Diagram (ER Diagram) or ERD?

Entity Relationship Diagram (also called as ER Diagram, ER Model, ERD) contains entities/attributes and relationships with those entities. ER Model is a methodological approach to create entities in normalized forms to minimise redundancy. It is drawn with the use of Data Modeling Tools and the following steps are done to create the entity relationship diagram.

  1. Understanding the business requirements
  2. Meetings / discussions with stakeholders (BA/SME/PM etc) to find out entities and relationships
  3. Data Modeler designs the ER diagram.

Data Modeling with ER Model:

In the above mentioned example,

1. Following entities are created by data modeler

  1. Department
  2. Gender
  3. Employee
  4. Salary Grade
  5. Degree

2. Then the data modeler adds the relevant attributes to those entities.

3. Creating attributes: Example Employee

  1. Employee ID
  2. Department Number
  3. Salary Grade Identifier
  4. Gender Code
  5. Degree Code
  6. Employee Name
  7. Birth DATE

4. The data modeler assigns relevant datatypes for each attribute based on the type of data stored:

Example Employee ID in employee entity

5. Relationships:

  1. After creating entities and attributes the data modeler decides how to create the primary key, foreign key
  2. Creating primary key:
    1. Example: Employee ID in Employee entity
  3. Creating foreign key:
    1. Example: Employee entity references Department entity, Gender entity, Salary Grade and Degree Entity

Optionality and Cardinality  options:

(Source: www.Erwin.com)

Creating foreign key:

  1. Example: Employee entity references Department entity, Gender entity, Salary Grade and Degree Entity

In The below ER diagram created from Erwin Data Modeling Tool by using Information Engineering (IE) notation, near to that department entity, one can see ZERO and ONE and near employee entity, ZERO AND ONE AND MORE. These symbols have specific meaning and the data modeler has assigned the right symbols due to business rules.

Similarly, entities are created in ER diagram and the data modeler gets the approval from the business team, technical to release the data models.

Data Modeling Software Tools Trial Versions:

Oracle has released “SQL Developer Data Modeler” and it is a free data modeling tool. If you want to become a data modeler, you can start designing data with “SQL Developer Data Modeler”.

Download ‘SQL Developer Data Modeler’:

https://www.oracle.com/database/technologies/appdev/datamodeler.html.

With Erwin and PowerDesigner, you can get the trial version.

Download Erwin:

http://go.erwin.com/erwin-data-modeler-free-trial

Download PowerDesigner:

https://www.sap.com/cmp/syb/crm-xm16-gam-it-dtcpdt/index.html

 

If you are interested to learn data modeling by using Erwin or SAP PowerDesigner or Oracle SQL Data Modeler, please reach us for more details – Training@learndatamodeling.com or 91-90801 57239.

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