A reverse index is a term used to describe the practice of reversing index values in a database management system before they are indexed. This process is specifically useful in indexing and accessing archived information that is organized in a sequential manner. Within transaction processing systems that have a high volume of data transmission, reverse indexing allows for database management systems to operate more quickly and efficiently.
There are three types of reverse index processes including b-trees, r-trees and bitmaps. B-trees are tree data structures that are responsible for the sorting of data as well as facilitating insertions, sequential access, and searches of the data. This process is also able to handle systems reading and writing huge data blocks. The internal nodes in a b-tree have multiple child nodes within a specific range and in the event that data is added or deleted from one node, the number of the child nodes changes. Internal nodes can be joined or separated to maintain the specific range.
A reverse index uses process key values before inputting the b-tree structures. The b-trees will put the same values within one index block, therefore improving the efficiency of the database when searching for a particular value. They also improve efficiency when looking up a value in a range.
An r-tree is a tree data structure that is similar to a b-tree. Unlike b-trees, r-trees are applied in spatial access methods. This means that r-trees are applied in the indexing of information with multiple dimensions. The r-tree has nodes, and each has several entries. Every entry inside of a non-leaf node contains two pieces of data, which is the method used in the identification of a child node, including all entries contained inside the child node.
A bitmap is a data selection structure that is responsible for the storage of individual bits in a compact manner. Bitmaps allow for increased efficiency and are responsible for increasing the operational speed of hardware devices. Many database systems are unable to manipulate single bits, thus making bitmaps one of the lesser used reverse index processes.
Overall, a reverse index is efficient in acquiring data from a database as quickly and efficiently as possible. Larger business enterprises regularly use reverse indexing techniques as a way to access critical information in a timely manner. Smaller business enterprises may find, however, that the cost of implementing a reverse index process may not be worth the increased functionality in their database management system.