in which different parts of the web have different capabilities cannot insist on bidirectional links.
Imagine, for example the publisher of a large and famous book to which many people refer but who has no interest in maintaining his end of their links or indeed in knowing who has refered to the book. In this case the link may be only of use to the person who made it.
However, there are cases in which the back-links are of great interest, and so they may be generated off line.
Another way is suggested by Phillip Hallam-Baker who "wondered about a tag being added to the get protocol to indicate where the text was being accessed from. This could then be used by intelligent servers to create back links - if this was desired. This would allow the wed to grow dynamicaly since I would know that logging onto any "key" W3 server I would be able to travel to all those parts of the web I was meant to..."
This method would also provide intersting statistics on the use of particular links, which would enhance the usage logging.