Module
One row of the locale-home course catalog. Includes the deterministic entry lesson so the home can link into the course without reading ports, every module so the home can list a course's progress lesson by lesson, and each lesson's progress slice so that progress is counted in the browser without a second round trip.
Reduce a lesson to its progress slice.
One lesson reduced to what progress accounting needs: which lesson it is, the module it belongs to, how long it runs, and its title and order so progress can be itemised lesson by lesson.