The skyline operator is the subject of an optimization problem, used in a query to filter results from a database to keep only those objects that are not worse than any other. This operator is an extension to SQL proposed by Börzsönyi et al. A classic example of application of the skyline operator involves selecting a hotel for a holiday. The user wants the hotel to be both cheap and close to the beach. However, hotels that are close to the beach may also be expensive. In this case, the skyline operator would only present those hotels that are not worse than any other hotel in both price and distance to the beach.