The author has done a excellent job. It describes about the important pieces in a dedicated chapter - XSQL architecture. After that he delves into SQL, PLSQL, XSQL , XSLT. The best part is chapter 14 on Building XSQL web applications. This explains how all the above pieces are put into a working model. The material is written keeping oracle 9i in mind. As a whole, I felt very comfortable reading the whole book.
Especially for database developers who come from sql, plsql background and are trying to get into web development world ( without the hassle of learning Java Servlets, Jsp etc ... ), I would definitely recommend it.