EJB3 entities are plain POJOs. Actually they represent the exact same concept as the Hibernate persistent entities. Their mappings are defined through JDK 5.0 annotations (an XML descriptor syntax for overriding is defined in the EJB3 specification). Annotations can be split in two categories, the logical mapping annotations (allowing you to describe the object model, the class associations, etc.) and the physical mapping annotations (describing the physical schema, tables, columns, indexes, etc). We will mix annotations from both categories in the following code examples.

EJB3 annotations are in the javax.persistence.* package. Most JDK 5 compliant IDE (like Eclipse, IntelliJ IDEA and Netbeans) can autocomplete annotation interfaces and attributes for you (even without a specific "EJB3" module, since EJB3 annotations are plain JDK 5 annotations).

For more and runnable concrete examples read the JBoss EJB 3.0 tutorial or review the Hibernate Annotations test suite. Most of the unit tests have been designed to represent a concrete example and be a inspiration source.