Neutral and absorbent elements Absorbent elements could be useful in RS to ensure that certain items always or never get recommended. For example, a UB
recommender could remove every item from consideration which has any features that score zero, or definitely recommend items which completely satisfy
one of the user preferences. T-norms and t-conorms each have absorbent elements. Incorporating functions with neutral elements into a recommender system
that aggregates user ratings (in either a CF or CB framework) allows values to be
specified which will not affect recommendation scores. A movie that is liked by
many people, for instance, would usually have its overall approval rating reduced
by someone who was indifferent toward it but still required to rate it. If a neutral
value exists it will not influence the aggregated score.