http://www.slideshare.net/gccutpl/slide-1022168
http://www.youtube.com/watch?v=ZMJZOfj-LGU
http://www.youtube.com/watch?v=Ij4hK4BF7Cc&feature=related
http://www.youtube.com/watch?v=eybyy4ch8ww&feature=related
http://www.slideshare.net/Ariasximena/informatica-10209243
