  Top-k and skylines are two important techniques that can be used to extract
the best objects from a set. Both the approaches have well-known pros and cons:
a quite big limitation of skyline queries is the impossibility to control the
cardinality of the output and the difficulty in specifying a trade-off among
attributes, whereas the ranking queries allow so. On the other hand, the usage
of ranking implies that ranking functions need to be specified by users and
renouncing the simplicity of skylines. Flexible/ restricted skylines present a
new approach to tackle this problem, combining the best characteristics of both
techniques making use of a new flexible relation of dominance.
