UC: lessons by period: dao
UC: create a lesson: controls the times for the lesson
UC: lessons by period: service
UC: lessons by period: UI
UC: lessons by period: GUI: aspect ratio
UC: lessons by period: GUI: getting the list of lessons
UC: lessons by period: GUI: parsing of the filter
UC: lessons by period: GUI: missing filter in the response
UC: lessons by period: transforming the lessons as events