Java Persistence API and o/r mapping metadata in JEE5 versus Cayenne?

[medips]

I'm a newbie in JEE5 and Cayenne but developed with WebObjects from  
2002 to 2005.
At first by reading the Java EE 5 Tutorial it appears that using  
annotations and other facilities it is easy to set up the object/ 
relational mapping in JEE5. So I would get a better picture to  
compare Cayenne with the standard JEE5 technology (which includes the  
Persistence API, the query language, Object/relational mapping  
metadata). Is Cayenne another way to do the mapping? Is the existance  
of Cayenne due to the lack of the current JEE5 facilities at start of  
the Cayenne project? What are the advantages and disadvantages of  
both methods?
Thanks to all the experts of both approaches!