An IArea is similar to an IBranch. They both provide transactional access to nodes, but the IBranch can only be used with an ITree. An IArea can be used with any INode. IArea is a higher level replacement for IBranch. The goal is to provide access to different independent models through one virtual model. It's like a unix filesystem with mount points. The model inside an area can also be an MPS model that is not a persistent data structure.