When you specify object-relational mappings using the JPA tools, the mapping information is contained in the Java™ class files in the form of Java annotations. However, you can also choose to define the object-relational mappings in XML in a file called orm.xml.
Mapping information defined in the orm.xml file automatically overrides both default JPA behavior and any mappings defined using annotations. Therefore, you can, for example, to adapt existing JPA entity beans to a different set of database tables without needing to modify the entity class files.
To edit the orm.xml file that is located in the META-INF directory of the JPA project: