What is a permuted index?

Question

I am reading Accelerated C++. I don't understand Exercise 5-1:

Design and implement a program to produce a permuted index from the following input. A permuted index is one in which each phrase is indexed by every word in the phrase.

      The quick      brown fox  jumped over the     fence The quick brown     fox                      jumped over the fence          jumped     over the fence             The     quick brown fox      jumped over     the fence                     The quick brown fox 

That explanation isn't clear to me. What exactly is a permuted index?

Answer 1

The term permuted index is another name for a KWIC index, referring to the fact that it indexes all cyclic permutations of the headings. Books composed of many short sections with their own descriptive headings, most notably collections of manual pages, often ended with a permuted index section, allowing the reader to easily find a section by any word from its heading. This practice is no longer common.

From: http://en.wikipedia.org/wiki/Key_Word_in_Context

ps: you can access wikipedia via http://www.proxify.com

Answer 2

You can find a 'live' example of a permuted index in the 7^th Edition UNIX™ Programmer's Reference Manual, Vol 1 (dating back to 1979). A fragment of it (from the PDF files) is:

If you look for 'account', you can find a number of related entries together. You probably wouldn't think to look for sa(1) as well as ac(1), not to mention acct(2) or acct(5) unless they were grouped together. This is the benefit of a permuted index; you can look up the key word and see it in a bigger context.

You could also look at the man page entry for the ptx(1) command in the same 7th Edition manual.