It is for the J2EE platform.If i am correct JAXB is used when mapping xml documents to java classes and vice versa.So it is useful when u develop web services
Technically this exam is not just a J2EE Web Services exam, its a Java Web services exam. In reality, the bulk of the questions are concerned with J2EE 1.4 Web Services. That said, the objectives clearly say that JAXB is in the exam as are architecture and design issues, so you'll need to be a bit broader than J2EE, but not much. The J2EE Web Services books along with the Blueprints will prepare you for most of the exam, you can supplement that by studying JAXB and other architecture, design and security documents.