From here, one should be able to get to the set of all messages from someone who claimed the name Chris Houck. Another reference to a message, probably less ambiguous. And if A is three hops away from D , then D is three hops away from A , and traversal in both directions should be possible. However, the object at the other end of the link does not necessarily encode the reverse path in its usual visual representation. All links must be bidirectional.
Folders have names.
Folders are sometimes arranged in a hierarchy. Each such message is a message in its own right, but the containment relationship can be important. Messages have bodies. The bodies can contain unstructured text. The bodies can contain text that is named , for example, an attached text file which has a file name or description specified in its attachment headers.