162 is within an interaction distance of the polygon 160 the projection of the closest edge of the polygon 162 onto the polygon 160 defines where two new vertices 162 a 162 b are added to the polygon 160 additional vertices 164 a 164 b may be created on the polygon 160 just outside of the new vertices 162 a 162 b 0053 fig9 e illustrates polygon 170 defined by four vertices 170 a 170 d fragmentation is performed by adding additional vertices 170 e 170 j around each corner vertex fragmentation generally involves the addition of new vertices between the vertices that define the end points of an edge segment the end points are generally not changed as will be appreciated each time a new vertex is defined a new edge segment is therefore created the definitions of the edge segments in the database are updated to reflect the new edge segments for layouts that include many levels of hierarchy in the database processing speed can be improved using parallel processing techniques where more than one processor is used each processor can analyze a different cell or level of hierarchy providing that before a particular level is analyzed any lower levels that are referenced in the level being analyzed are completed first topological sorts can be.