what is data modelling and ER diagrams?

Hi
what is data modelling and ER diagram ?

Check this out...

ER diagram ...

http://www.samoore.com/teach/db/er/index.php

More information here...

http://www.dmreview.com

data Modelling adn Entitity Relation Diagrams are pictorial representaion of all the selected tables ( with their columns , some copnstarints , constraints , ) relationship with other tables and type of relation ship ata glance .

Data Model Diagram is similar to this . it tells about the workflow of any user created application or procedure .

this is used by designers while designing any application . there is a seperate tool to prepare server model diagram , ER Diagrams , Functional Hierarchy Diagrams , Data Model Diagram