For several reasons, nn interacts with users in a very different way than xrn. The first difference is that being text based, nn requires users to memorize key stroke commands rather than presenting them with a graphical display of buttons to press. The second main difference is that nn uses a two tier presentation scheme. For each newsgroup to which the user is subscribed, he is first shown a list of the subjects for all the available articles in the newsgroup. At this point, the users selects which articles to read based on the subjects of the articles. Next, the selected articles are shown to the user, with the unselected articles being skipped over.
Figure: The second tier in the nn interface: reading the
selected articles. Users are reminded to vote by the line at the bottom.
Figure: The first tier in the nn interface: selecting the
articles to read. The highlighted article marked with a `$' has been
autoselected by the collaborative filtering system.
A picture of the ``article selection'' tier from the nn
interface is shown in figure 
. In the modified
nn, the collaborative filter is run whenever a user enters a
newsgroup. The most popular articles among the ones displayed are
automatically selected by the collaborative filter, so that if the
user wants to read only the popular articles she can go directly
into the article reading tier. If the user wishes to, she can change
the number articles autoselected by the filtering system, or manually
select and unselect articles as in the unmodified nn. The
interface displays at the bottom of the screen how many articles were
autoselected by the filtering system, and can also show the user a
list of only the selected articles.
Once the user has moved into the second ``article reading''
tier of the interface, the display changes to look like that of
figure . We attempt to remind the user to vote for
articles by placing a line at the bottom of the screen describing the
voting keys. nn is extremely configurable, and by setting a
variable users can select an auto-advance on vote mode similar to the
one implemented for xrn. With this mode set, users are
automatically sent to the next screen of text or the next article
after voting so that voting on an article requires no more key strokes
than simply reading that article does. More information about the
collaborative system is available to the user from the help menus, and
from the message-of-the-day displayed at nn's startup.