One-to-many Relationships in WordPress
WordPress is exceptionally flexible when it comes to changing existing behaviors and implementing new ones, and with aid of the multitude of API’s many things are possible.
When you start extending the default data structures in WordPress, most of the time you’ll be extending Posts, either default Posts (or Comments) or Custom Post Types, other times might be extending User objects. Extending would most of the time mean adding more data which you can query by and pivot around.