In an interview with Lucas that I read, he explained that originally he was going to do the whole saga in a narrative style and 'The Journal of the whills' was going to be the title for it. Then after actually starting the novel and going through script changes, he used 'The Journal of the Whills' as a guideline for the rest of the saga. It was supposed to be some entity called the whills that documented the major happenings in the SW galaxy. If you read the book 'The Annotated Screenplays it goes into this idea more and shows just how much the script changed. Mace Windu was originally going to be the central character!