How the following cubic spline function is derived?

In most of the research papers on meshless methods the following cubic spline function is used as weighting function.

 w(y) = 0  if y < -2,

w(y) =1/6(y+2)^3  ,    if -2 < y < -1 

w(y) =  2/3 – y^2(1 + y/2) ,  if   -1 < y < 0

w(y)=   2/3 -y^2(1 - y/2) , if   0 < y < 1

w(y) = -1/6 (y – 2 )^3  ,   if    1 < y < 2

w(y) = 0 if y >2

I wish to know why this particular function is used? How this function is obtained?