In this paper

the clustering of BBL is researched. A （extended） vertex structure model

a graph model and an （extended） oriented tree model are proposed. A formula calculating the number of vertex structures （or oriented trees） is obtained. A conclusion that the （extended） vertex structure and the （extended） oriented tree is one to one correspondence is proven. Clustering algorithms used in top-down placement and floor plan and bottom-up placement are presented. A placement algorithm adopting recurrent clustering which can form slicing and nonslicing placement is proposed. These algorithms have been implemented on UNIVAC 1100/10 computer in Fortran 77. The experimental results are satisfactory.