This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
The orm.xml file is an option to use to map your entities instead of using annotations, if you are using annotations then you do not need it.
The persistence.xml should technically list all of the persistent classes using the <class> tag, but if all of your classes are in the same jar file as your persistence.xml, then these will be discovered by default in JEE,
and in JSE if you set <exclude-unlisted-classes>false</exclude-unlisted-classes>.