When I buy a dvd I usually watch the extra's which often includes the screenwriter expaining how they set about condensing the story. The guy that did The Time Travellers Wife explained how he knew he needed to 'lose' 4/5ths of the story and characters and only keep what was relevant [thought he did an excellent job]. Perhaps doing a screenplay for a book which then becomes a musical is slightly easier because you don't have to create the image of the characters? Was terribly disappointed with The film of Captain Corelli's Mandolin, mainly because they made Pelagia do things in the film that were out of character, and that made me angry, and they missed out the bit where Mandras swam out to sea with the dolphins [a screenwriters dream I would have thought]. If you write a rubbish book all that happens is nobody buys it and you don't make any money, whereas a screenwriter is constantly looking over their shoulder and finding lots of potentially angry people .