From the user stories:
1.
As a Privacy Officer I want to be able to add and edit the categories of personal data in my institution.

Moodle should provide a report listing categories of personal data, with options to edit existing items, or create new items.
Only users with relevant capability should be allowed to add/edit.

2.
As a Privacy Officer, I want to be able add and edit the purposes for collection of personal data in my institution.

Moodle should provide a report listing purposes for capturing personal data, with options to edit existing items, or create new items.
Only users with relevant capability should be allowed to add/edit.
I should be able to provide a default value for retention period during this add/edit process.

When creating a purpose there should also be a checkbox or something similar for stopping user deletion requests from being granted. Some purposes such as keeping grades has a higher standing for retention above the right to be forgotten. This flag would ensure that the areas that use this purpose do not have user data deleted from user's making such requests.