Bitmap Indices (Cont.) Bitmap indices are useful for queries on multiple attributes not particularly useful for single attribute queries Queries are answered using bitmap operations ·Intersection(and） ·Union(or) Complementation (not) Each operation takes two bitmaps of the same size and applies the operation on corresponding bits to get the result bitmap ·E.g,100110AND110011=100010 1001100R110011=110111 NOT100110=011001 Males with income level L1:10010AND 10100=10000 Can then retrieve required tuples. Counting number of matching tuples is even faster Database System Concepts-7th Edition 24.13 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 24.13 ©Silberschatz, Korth and Sudarshan th Edition Bitmap Indices (Cont.) ▪ Bitmap indices are useful for queries on multiple attributes • not particularly useful for single attribute queries ▪ Queries are answered using bitmap operations • Intersection (and) • Union (or) • Complementation (not) ▪ Each operation takes two bitmaps of the same size and applies the operation on corresponding bits to get the result bitmap • E.g., 100110 AND 110011 = 100010 100110 OR 110011 = 110111 NOT 100110 = 011001 • Males with income level L1: 10010 AND 10100 = 10000 ▪ Can then retrieve required tuples. ▪ Counting number of matching tuples is even faster