my $deps = { 'mainpackage-1.0' => [ 'dependency1-1.3',
                                    'dependency2-2.3',
                                    'dependency3'],
             'dependency1-1.3' => [ 'dep1_of_dep1' ],
             'dependency2-2.3' => [ 'dep1_of_dep2',
                                    'dep2_of_dep2',
                                    'dep3_of_dep2' ],
             'dependency3' => undef };