Hello, I am learning DDD and I am a little bit lost in Infrastructure layer:

As I understand, "all good DDD applications" should have 4 layers: Presentation, Application, Domain and Infrastructure. Database should be accessed using Repositories. Repository interfaces should be in Domain layer and repository implementation - in Infrastructure (reference http://stackoverflow.com/questions/693221/ddd-where-to-keep-domain-interfaces-the-infrastructure).

Application, Domain and Infrastructure layer should/may have services (reference www.lostechies.com/blogs/jimmy_bogard/archive/2008/08/21/services-in-domain-driven-design.aspx), in example EmailService in Infrastructure layer which sends Email messages.

BUT, inside Infrastructure layer we have repository implementations, which are used to access database. So, in this case, repositories are database services? What is the difference between Infrastructure service and repository?

Thanks in advance!