The first two sections of the book cover a variety of technologies. You should be familiar with many of the them, but you may not be familiar with all of them. As an EJB programmer, you probably know J2EE technologies like EJB and JNDI well, but you may not be familiar with JDO. This section provides a JDO tutorial just for you. Because you know EJB and JNDI so well, however, you will find no use for the J2EE tutorial.
In short, not every tutorial chapter is for every reader of this book. Some advanced readers, in fact, will have no use for any of the tutorial chapters. I do expect most readers will find the need to reference at least one of these chapters before tackling a chapter earlier in the book. If you have no experience in JDO, for example, you probably want to look at the JDO tutorial before reading the chapter on JDO persistence. If you have no EJB experience, read the J2EE chapter before tackling either of the EJB persistence chapters. Finally, you need to understand the material in the JDBC and SQL tutorials to appreciate just about any chapter in Part I or Part II.