I started working on support for sets but soon realized that support for collections in general was basically non-existent. So I started working on that. Here is what I have so far if anyone wanted to look it over: https://github.com/sebersole/hibernate-core/tree/HHH-6503 It is still early on, but the basic ideas are there. Basically, I break down the "source" aspect of mapping collections into the individual pieces or information we need about persistent collections: 1) general meta about the collection (java type, hibernate type, etc) : PluralAttributeSource 2) info about the collection key : PluralAttributeKeySource 3) info about the collection elements : PluralAttributeElementSource eventually we will need to describe the key/index of maps and lists, but this is a start. -- steve(a)hibernate.org http://hibernate.org