http://delivery.acm.org/10.1145/1370000/1367629/p979-wang.pdf?ip=140.159.2.227&id=1367629&acc=ACTIVE%20SERVICE&key=65D80644F295BC0D.0C46C0738E05A806.4D4702B0C3E38B35.4D4702B0C3E38B35&CFID=664406535&CFTOKEN=43295823&__acm__=1429252267_d5b11626ef312c9c4f231d779a060504