> Subfield $a is used for the host name when the elements of the URL are
> parsed into separate subfields.  The host name is the first part of the
> URL following by the access method, a colon and 2 slashes.  Subfield $u is
> defined as a URL, and it wouldn't be appropriate to include a subdirectory
> and filename.

This wasn't stated very clearly. What I meant to say is that it is not
appropriate to include only the subdirectory and filename in $u, since $u
is supposed to contain a complete URL that systems can use for linking.
I'm not sure how splitting up the locator will make it easier to keep the
links up to date.

Rebecca