  Ranking (or top-k) and skyline queries are the most popular approaches used
to extract interesting data from large datasets. The first one is based on a
scoring function to evaluate and rank tuples. Its computation is fast, but it
is sensitive to the choice of the evaluating function. Skyline queries are
based on the idea of dominance and the result is the set of all non-dominated
tuples. This is a very interesting approach, but it can't allow to control the
cardinality of the output. Recent researches discovered more techniques to
compensate for these drawbacks. In particular, this paper will focus on the
flexible skyline approach.
