-- a simple topicmap-ish relation table.

table tm_relations {
id       int auto_increment
type     varchar              -- TM instanceOf (eg, actor-film)
subject  varchar              -- TM topic (topic of current page/view)
subjRole varchar              -- TM roleSpec (eg, actor)
object   varchar              -- TM topic (object of association, 
                                 -- eg, "TO Kill a Mocking Bird")
objRole  varchar              -- TM roleSpec (eg, film)
}

-- roles are useful because topics may have multiple roles, eg, Gregory Peck
-- is/was(?) an actor, a father, a producer, a teacher, etc.



-- an RDF-like approach is very simply based on triples: Subject, predicate, 
-- object. it's amazing how powerful this simple construct is. The predicate
-- does all the work.
-- eg, {GP, is-actor-in, TKMB} for GP as subject; 
-- eg, {TKMB, has-actor, GP}   for TKMB as subject;

table rdf_relations {
id       int auto_increment
subj     int                  -- node_id
pred     varchar              -- or an id in predicate table (more normalization)
obj      int                  -- node_id
}

-- To get all relations for GP:
--       Select * from rdf_relations where subj='GP' order by pred;

-- You'll probably want to create a link for the object, so you'll want to
-- join with the node table on object to get node_id (or other needed link
-- creation information). Then, you output with 
-- (pseudo code): foreach $result, echo $pred [link:$obj].

-- Since the RDF concept is so simple and immediately intuitive, it may be a
-- good choice for an initial relation module. It can also be easily extended
-- later into richer TM while preserving the original fields and data.