Hadoop is targeted at BigData.<p>For instance, if you are a financial institution that generates a lot of transactions, how do you data mine the transactions to find out what type of customers could purchase more services from you?<p>Another example is Facebook. How does it generates activity streams of your friends and your friends' friends? SQL probably isn't the best choice.<p>RDBMS's whose forte is in transaction processing, isn't as fast when it comes to answering questions like this. Hadoop and its competitors in this space are hoping to generate revenue from selling software and services for this.