Tasks to update collections

From the milestone 2 requirements:

MUST: Have a mechanism that triggers tasks to update a “collection” so it is kept in sync with another collection (add missing keys, drop outdated keys)
  That mechanism might be a workflow step.
  Design of atomic updates ? Naming of collections ?

We'll need to make more progress on the fundamentals of collections and workflows before we can get very far with designing this, but we'll need to bear it in mind as a major use case for both of those.