B+-tree (1)
< P1, K1, P2, K2, P3, .. , Ki-1, Pi, Ki, .., Kq, Pq+1 >
q values and q+1 pointers
i-child values K : Ki-1 < K =< Ki
?p/2 =< q =< p
p is the entry blocking factor
no minimum for the root
< Pr1,K1, Pr2, K2, .. , Pri-1, Ki-1, Pri, Ki, .., Prq, Kq, Pnext bloc >