+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
              |SFI11| |SFI12| |SFI21| |SFI22| |SFI31| |SFI32|
              +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
                  \    /          \   /           \    / 
   +----------+   +----+         +----+          +----+    
   |Classifier|---|SFF1|---------|SFF2|----------|SFF3|
   +----------+   +----+         +----+          +----+