"Best practice" advice

I'm developing the second stage of a database that will eventually be used
to model networks of references between documents.  I already have a table
of core documents, and the next step is to track what documents each of
these core documents refers to. (Is this confusing enough already?)

The relationship is one-to-many, and I can handle that fine. The issue
is: some of the references in the core documents will be to other core
documents. Other references will be to documents that are not in the core
documents table.  I need to track whether the document referred to is
in the core table or not. The question is how best to capture this.  Ideas
I have are:

1.) A single referrals table that can track both kinds:
referring_id      --> serial number of the referring core document
referred_title
referred_author
referred_date
referred_page
referred_id       --> serial number of the referred document if it's in                     the core table; otherwise
NULL


2.) Two referrals tables:
referring_id                  referring_id
referred_title                referred_id
referred_author
referred_date
referred_page


3.) A "peripheral documents" table and a referrals table:
periph_id                     referring_id
title                         referred_table
author                        referred_id
date
page

Comments?

Thanks.

----------------------------------------------------------------------
Andrew J Perrin - http://www.unc.edu/~aperrin
Assistant Professor of Sociology, U of North Carolina, Chapel Hill
clists@perrin.socsci.unc.edu * andrew_perrin (at) unc.edu