Sets and Named selections both represent a selection of records. Among the differences between the two are:
• A named selection is an ordered list of records; a set is not.
• Sets are very memory efficient, because they require only one bit for each record in the file. Named selections require 4 bytes for each record in the selection.
• Unlike sets, named selections cannot be saved to disk.
• Sets have the standard Intersection, Union and Difference operations; named selections cannot be combined with other named selections.