week_number_systems which holds things like ISO 8601, US Sunday etc. Then, we run a task to populate another table called week_definitions. The week definitions table has each row represent a week, and a week number system can have many week definitions (one to many). This is so that our app's schedule is dynamic, and can support any type of week.starts_at and ends_at, as well as a year and week (because 1 day, can have have a different week number or year as per ISO 8601 or US Sunday).