Avoiding loops and crossing edges in the final graph, which                     
directly results in a tree where you can follow the edges from                  
one author.                                                                     
                                                                                
Of course some SOB links will be lost, but that is the tradeoff.                
What will definitely be retained is:                                            
                                                                                
 - the author's existence and his attachment to one                             
   subsystem s/he contributed, though probably not the one                      
   with the major number of contributions                                       
                                                                                
 - gatekeeper positions in the tree (but by chance only)                        
   you can expect to find Andrew and Linus near the tree root                   
                                                                                
What could be improved as I think about the issues...                           

 - count the number of submissions to a particular upstream                     
   person and instead of longest-chaining, do "weighted-chaining";              
   essentially stacking a contibutor into the subsystem he                      
   contributed most to.                                                         
