How do providers, categories, feeds and entries correlate?
And authors on top of that?

Authors are simple: each entry is linked to one author, even if the
author is the same the objects differ. We can change this in the future,
right now there is no need to do that.
The other objects are a bit more difficult.

DXS: provider -> category -> feed/list -> entries
GHNS: provider -> feed [with categories] -> entries

Example
-------

The maintainer of an application offers extensions in the categories
"image" and "script". Since the application has a lot of users, both
kde-coolextensions.org and kde-betterextensions.org offer such extensions.
The provider.xml file would thus contain the two <provider>s. When fetching
the feed files for most popular/most downloaded/most recent, those files
need to contain entries of *all* categories! A workaround is to add virtual
providers for each category (there won't be much difference in the UI), but
ideally with frameworks such as Hotstuff the right number of items will be
inserted into the feed.
With DXS, the problem doesn't exist since DXS fetches all categories first
and then the feeds for each category. DXS also allows to retrieve all entries
of a certain category, so it is much more flexible in general.

GHNS setup:
-----------
 provider kde-coolextensions.org
  feed most-recent
   entry a [category image]
   entry b [category script]
   ...
  feed most-downloaded
  ...
 provider kde-betterextensions.org
  ...

Alternative GHNS setup:
-----------------------
 provider kde-coolextensions.org/image
  feed most-recent
   entry a [image]
   entry c [image]
   ..
  ..
 provider kde-coolextensions.org/script
  ...

DXS setup:
----------
 provider kde-coolextensions.org
  category image
   feed most-recent
    entry a [image]
    entry c [image]
    ...
   ...
  ...
 provider kde-betterextensions.org
  ...