music_data record, music_data_type direction.

Many-to-one join to direction_type_list, foreign key direction_id. Each direction_type_list record joins to a list of direction_type objects.

A direction music_data_type record in the music_data table represents a direction element, and a direction_type_list record represents a direction-type element. Individual subelements of direction-type are stored in the direction_type table.

Field sound_id is a join to a sound record, which is also in the music_data table, music_data_type value sound.

Field listening_id is a join to a listening record, which is also in the music_data table, music_data_type value listening.