Bitmap Indices Bitmap indices are a special type of index designed for efficient querying on multiple keys Records in a relation are assumed to be numbered sequentially from,say,0 Given a number n it must be easy to retrieve record n Particularly easy if records are of fixed size Applicable on attributes that take on a relatively small number of distinct values E.g.,gender,country,state,... 。 E.g.,income-level (income broken up into a small number of levels such as0-9999,10000-19999,20000-50000,50000-infinity) A bitmap is simply an array of bits Database System Concepts-7th Edition 24.11 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 24.11 ©Silberschatz, Korth and Sudarshan th Edition Bitmap Indices ▪ Bitmap indices are a special type of index designed for efficient querying on multiple keys ▪ Records in a relation are assumed to be numbered sequentially from, say, 0 • Given a number n it must be easy to retrieve record n ▪ Particularly easy if records are of fixed size ▪ Applicable on attributes that take on a relatively small number of distinct values • E.g., gender, country, state, … • E.g., income-level (income broken up into a small number of levels such as 0-9999, 10000-19999, 20000-50000, 50000- infinity) ▪ A bitmap is simply an array of bits