Block-nested-loop (BNL) algorithm Nave algorithm   Compare each object with every other object   Only if no object dominates it, then it is a sklyline   Maintain a window of objects not yet dominated Check every new object against the list   If object is dominated, prune it   If object dominates some point(s) in window, prune those object(s)   If neither, add to window Window contains the skyline objects What if window does not t in memory?   Put into temporary le and note timestamp   Objects added afterwards are not guaranteed to be skylines   Make extra pass using the temporary le as input