Entity Relationship Diagram

Today we had a lecture on Entity Relationship Diagrams which are a diagram system that explain he relationship between the entities on a database.

I also found some other definitions online to be able to understand this concept further:

“An entity-relationship diagram (ERD) is a type of data modeling that shows a graphical representation of objects or concepts within an information system or organization and their relationship to one another.”

Source – What is entity relationship diagram? – Definition from WhatIs.com. 2015.What is entity relationship diagram? – Definition from WhatIs.com. [ONLINE] Available at: http://searchcrm.techtarget.com/definition/entity-relationship-diagram. [Accessed 23 February 2015].

The diagram below describes what each of the symbols are and how to use them in an ERD.

Source – http://docs.oracle.com/cd/A87860_01/doc/java.817/a81358/05_dev1.htm

Here is a basic example of a real ERD as a purchase order application:

Source – http://docs.oracle.com/cd/A87860_01/doc/java.817/a81358/05_dev1.htm