Explanation:
Prior to Oracle9i, you could create bitmap indexes on a single table. Bitmap indexes are very useful in data warehousing environment for low-cardinality columns. Oracle9i extents this concept to a bitmap join index that optimizes the joining of two or more tables. A bitmap join index is a space- and performance-efficient technique. By predetermining associations, bitmap join indexes eliminate the large volumes of data generated with Cartesian products performed in a join operation.
Incorrect Answers:
1: A bitmap join index is not a join of two bitmap indexes on a table.
3: A bitmap index created on the join of two or more tables, not indexes.
4: You cannot reference an IOT or a temporary table.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 142-143
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 54-56
Chapter 2: Oracle9i Architecture Changes

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