+----------MOD_ATT:N-N---------+            
      |           +----MOD_ATT:N-N---+            
      |           |     +-MOD_ATT:N-N+SUBJ:V-+    
      |           |     |            |       |    
 Association of cell surface and __NODE__ occurs .
MOD_ATT:N-N (__NODE__,association)
MOD_ATT:N-N (__NODE__,cell)
MOD_ATT:N-N (__NODE__,surface)
SUBJ:V-N (occur,__NODE__)