double lookup index

n. An index that points to another index, requiring users to check two sources to locate the information they seek. ComputingThe simultaneous use of two indexes for greater precision in locating data.


An example of a double lookup index1 includes a classified index, which requires users to first consult a list of classes to determine the class (often a number) under which relevant information is indexed. The Domain Name System (DNS) is another example of a double lookup. Computers connected to the Internet are addressed using an Internet protocol (IP) address. Because numerical addresses are not mnemonic and because the IP address may change frequently, users are typically given a Uniform Resource Locator (URL), such as Applications submit the URL to a DNS server, which returns the IP address necessary to connect to the desired machine. - An example of a double lookup index2 includes the use of a column and row headings to specify a cell.