go
                                                                             /I\
                                                                            / I \
                                                                           /  I  \
                                                                     I---src pkg bin
                                                                     I       /\
                                                                 keyboard_1 /  \
                                                                   I      mod   sumdb
                                                                main.go    I      I
                                                                the whole data   the whole data