Why Use Relational Databases? by Greg O'Lone, Stretched Out Software, Inc.

Lets use an example of a real estate agency which wants to keep track of every property they have for sale and the agents responsible for showing those properties.
If you were to store this information in a flat file, all of the agent info would be stored over and over for each house they are responsible for. Now imagine if that agent had 100 houses...we'd be storing his/her info 100 times and if it ever changed, we would have to change 100 individual records.		In a relational database, you only want to store each piece of data once, so you create additional tables for the otherwise redundant data and then link the info together. 100 houses each with a link to a single agent record. A change in the agent record would mean ONE update.
Houses HouseID Address City State Zip Asking Price Options AgentName AgentAddress AgentCity AgentState AgentZip AgentPhone AgentCel AgentEmail AreaOfTown		Agents Houses Area AgentID HouseID AreaID Name Address Name Address City   City State   State Zip   Zip Asking Price   Phone Options   Cel AgentID   Email AreaID