Fowler on List and Hash

Interesting article, as we move towards MongoDB at work this is timely information for me.

A strength of the list and hash structure is that you can manipulate it with generic operations which know nothing of the actual keys present. These operations can then be parameterized with the keys that you wish to manipulate. The generic operations, usually arranged into a collection pipeline, provide a lot of navigation features to allow you to pluck what you need from the data structure without having to manipulate the individual pieces.

http://martinfowler.com/bliki/ListAndHash.html