Using and Understanding Java Data Objects is an application programmer's guide to the Java Data Objects (JDO) specification recently accepted by the Java Community Process. JDO provides a universal and transactional persistence service for objects. JDO will store and retrieve objects of nearly any application defined class using any data storage technology for which a JDO implementation is available. JDO completely encapsulates the details of the underlying data storage technology that is used. JDO has its own query language (JDOQL) that allows the programmer to find objects based on the fields and relationships of the object model. The syntax of JDOQL is similar to the syntax of Java itself. JDO increases programming productivity by simplifying and minimizing the code that must be written to store and retrieve object state. The use of JDO also allows the application to be ported across different data storage technologies. Like the servlet and EJB specification, JDO is a standard that will be implemented by competing software vendors. Several JDO implementations are currently available as third party products for relational databases and object oriented databases. Using and Understanding Java Data Objects is a guide to the features and uses of JDO. Part I is a guide to the JDO API, the JDO metadata, and JDO's byte code enhancement. Part II explains the use of JDO in several application deployment scenarios, including stand-alone, client-server, servlet, and EJBs. Part III is a tutorial explaining the example programs and learning tools supplied with the book.