Via Matt, a comparison between Hibernate’s HQL and JDO’s OQL. I’m still not sure which one to use; I don’t like JDO too much and it doesn’t look like it’s gaining much popularity. Besides, I don’t think there is a convincing Open Source implementation of JDO. Another cool-sounding alternative I have to play with: Prevayler, as featured recently on Slashdot, is an in-memory transparent object-persistence layer. Their site is still slashdotted, apparently.