Modelling relationships

Hi,
I am wondering how Postgres can support the modelling of various
relationship types apart from defining primary and foreign keys which is
the pure relational solution.
I am doing a project to explore the capabilities of an Object Relational
system just like Postgres, and compare them with those of a pure relational
system. I am doing this using a Protein Interactions database (biology
stuff..)
I am looking at how to model various relationship types
 for example, a table type A is related to many table types B. For this
case, I defined
  create table B
  (...........)

  create table A
  (manyBs B)

  a)When inserting values into column 'manyBs' it stores what looks to me
as
a pointer (eg values 2352192 of type B). How can I use this value to
perform useful queries?
  b)Does Postgres support REFerence column types to represent one-to-many
relationships as a substitute for primary/foreign keys? If yes, does it
have a DEREF operator to dereference a value of REF type and thus access
the object pointed to by REF?

If somebody came across these before, could he/she give me some help?

Kostas Vassiliadis