Why does the Google App Engine documentation emphasize JDO over JPA?

Most of the docs for Google App Engine are written for JDO. Only one pa开发者_如何学Goge of docs are devoted to using JPA. Is this because JDO is more suited to App Engine or was there some other reason for the preferential treatment given to JDO?

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JPA is oriented towards mapping java objects onto relational databases. App Engine is not a relational database. JDO is more agnostic about the backend you persist objects to, so it is a better fit.

Update: I should mention that the JPA/JDO debate can get heated sometimes, like in this previous question for example.