Roger S. Baum, the great-grandson of L. Frank Baum, discusses carrying on the world of Oz. The Springfield, Mo., resident has written 14 children’s books set in Oz, with a 15th in the works. An animated musical based on his first book, “Dorothy of Oz,” will be released in 2010. This year marks the 70th anniversary of the release of the classic 1939 film “The Wizard of Oz.”