1. Introduction
The explosion of information has been a continuous trend since the 1970s, partially being triggered by Internet rapid development and also its associated information and communications technology (ICT) penetrating every part of the world and our daily life. The three Vs (volume, variety, and velocity) from today's big data however are unprecedented. Our world is generating data at a speed faster than ever before. In 2010, 5 Exabyte (1018 bytes, 1 billion gigabytes) of data had been generated every two days, beyond the total amount of data being generated by human from the dawn of civilization to 2003 [1]. By the year of 2020, over 40 zettabytes (1021 bytes) of data is estimated to be generated, replicated and consumed [2]. With these overwhelming amount of data pouring into daily lives, from anywhere, anytime, and any device, we are undoubtedly entering the era of big data.