L. Tan, R. S. Lou and G. Q. Xu. In the Journal of Computers. Vol. 20, Page 105-110, 1997.

Geometry method has been proven as an sucessful way to study the safety problem of scheduling two transations. We extend it to N dimension space to handle the arbitrary number of concurrent transaction. The forbidden area in the case of two transitions will be therefore generilized as a prism in N dimension space. We give a sufficient condition for ensuring seriability of N transitions. Consequently the polcy based on this condition, called BOLP, extends traditional two phrase locking policy to schedule N transactions safely.