JDO provides transparent persistence management. It means that a Java developer does not need to write any code for managing the persistence of business objects.
JDO 1.0 does not specify a standard way of defining O/R mapping. Each JDO implementation uses a different O/R mapping format. Most of the products offer limited O/R mapping possibilities.
JDO supports inheritance and navigation between objects.
JDO and Entity Bean are complementary. If you plan to use persistent objects locally without an application server or if you always access data through Session Beans, it is better to use JDO. If you need to use remote persistent objects or need better security support, you should use Entity Beans.
There are several commercial and open source implementations of JDO. For up to date information, see the websites http://www.jdocentral.com and http://java.sun.com/products/jdo/.