SQLf vs. Skyline - Expressivity and Performance

SQL has limitations in order to express user preferences. The ORDER BY clause is a way to express preferences, but it is complicated to manage criteria that involve three or more conditions. Skyline operator is a simple way of specifying user preferences extending SQL, but has high processing time when its algorithms are evaluated. SQLf is another SQL extension for user preference based on fuzzy logic whose algorithms can be less expensive. This work compares SQLf and Skyline approaches in terms of time and number of returned answers. Also, we compare the expressive power of both SQLf and Skyline languages.