Most of the transactions have been computerized in day to day life, which in turn produces lot of digital data. For example point-of-sale, internet shopping & browsing, credit cards, information on credit cards, purchase patterns, payment history, sites visited etc. One trip by one person generates info on destination, airline preferences, seat selection, hotel, rental car, name, address, restaurant choices and so on. Data size is so huge that it cannot be processed or even inspected manually. Automated data collection tools and mature database technology lead to tremendous amounts of digital data stored in databases, data warehouses and other information repositories. Vast quantities of data are collected and stored out of fear that important information will be missed.