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. The bodies can contain binary objects which, while not textually searchable, are named and described.
Bodies can contain hyperlinks.
Plain-text messages might happen to have detectable URLs in them, and HTML messages have many mechanisms for referring to other objects. This implies that it would be interesting to traverse from a message, to information about a web page that it refers to, and back to a set of messages which refer to objects on that server. Following a link only gives you one dimension of mobility. Any link-relationship should be searchable. All messages from person which contain a message from person .