I'm starting to get the point. But new questions start to arose in my mind.

Let's take a social website like Facebook. If you edit your personal information, you will see there are lots of information to edit. When you start to edit your "Education and Work" info, you will see that you can add as many "Job Information" as you like. No matter how many you add, you have the chance to add infinite (or maybe finite??) job information. So, if you don't use EAV model, what would you use to implement such a feature? I'm sure Facebook don't temporarily become unavailable when they add a new field for the users.

Facebook have more than hundreds of fields to edit. If I can understand the model that websites like Facebook use, I'm sure I will find a suitable solution.

Btw, your answers are always perfect guides for me. I really learn so much, so thanks a lot.