Opensource Object Oriented Database for WPF application

I am planning to implement an application using WPF, I want to use an Object Oriented database.

Could you suggest an Open Source Object Orien开发者_如何学Goted Database?

Thanks

Try db40 http://www.db4o.com/

they have a GPL version

if you wanna look for something else -

http://en.wikipedia.org/wiki/Comparison_of_object_database_management_systems