We are working with Epics, Stories and Subtasks. However, as far as I understand it, technical tasks (e.g. DB normalization) should not be user stories as there is no direct value visible to the customer and hence it should be marked as Task - if I understand, Task can be at the same level as story?
But if we start using Tasks, then the burndown will not reflect the reality as all stories might be done but technical tasks still in progress, which will not be visible.
Or is there a better way of working with technical tasks in SCRUM?