There is a function similar_text() in the PHP library. The documentation (http://php.net/manual/en/function.similar-text.php) tells me that "This calculates the similarity between two strings as described in Oliver [1993]."
Despite extensive searching, I can't find the paper that "Oliver [1993]" is referring to; nor any candidate for who "Oliver" might be. The PHP source is undocumented. The only other reference to Oliver 1993 is in a forum at http://www.codeguru.com/forum/showthread.php?t=41089, and I think that information is derived from the PHP documentation.
Anyone aware of what this might be?