Indexing Technical Documents: An Interview with Lori Lathrop
http://www.writing-world.com/tech/indexing.shtml

Vega, Barbara
Writing World
2001

Abstract:

Indexes are as important to your documentation as your documentation is to the product. Just as it would be difficult, if not impossible, for people to use your product without any documentation, it is equally difficult for people to use documentation without a good index.