Collecting large-scale multi-criteria rating data. Multi-criteria rating datasets
that can be used for algorithm testing and parameterization are rare. For this new
area of recommender systems to be successful, it is crucial to have a number of
standardized real-world multi-criteria rating datasets available to the research community. Some initial steps towards a more standardized representation, reusability,
and interoperability of multi-criteria rating datasets have been taken in other application domains, such as e-learning [98].
In this section we discussed several potential future research directions for multicriteria recommenders that should be interesting to recommender systems commu-
nity. This list is not meant to be exhaustive; we believe that research in this area is
only in its preliminary stages, and there are a number of possible additional topics
that could be explored to advance multi-criteria recommender systems.