Object-relational mapping or ORM is the category of products that provide services to map objects to relational databases. The Java Persistence API (JPA) is the Java specification that provides a standard to ORM in Java. JPA provides both a standard mapping definition (through annotations or XML) and a standard runtime API and object-level query language (JPQL).
EclipseLink provides sophisticated and high performance object-relational mapping services and complete support for the JPA specification. JPA objects are mapped through the package javax.persistence annotations and JPA persistence.xml and orm.xml. EclipseLink also provides extended annotations through the package org.eclipse.persistence.annotations. JPA provides a runtime API through the EntityManager class in the javax.persistence package.
EclipseLink also provides a POJO ORM API and mapping model which its' JPA support is based on. The mapping model classes are in the org.eclipse.persistence.descriptors and org.eclipse.persistence.mappings packages, and sessions.xml and project.xml files. The runtime API in provided through the Session and UnitOfWork classes in the org.eclipse.persistence.sessions package.