oid dependency question...

Hi all...  I just jumped on the postgres boat for a new project and I have a
sort of 'design / theory' question.

I am building a web application and I want to store pieces of the output in the
database as large objects so that I don't have to recalculate them (I am
predicting a sizeable CPU overhead for generating the pages...).  So, lets say
I render page X which contains a list of 10 items that were queried out of a
bunch of different tables.  Now I take that rendering and store it in my cache
table...  this is fine, but if any of those 10 items are changed I want the
cache entry to automatically expire so that the page is recalculated next time
it is requested.  In another case a page will be dependent on the table itself
(such as the insertion of a new record...).

So far, I have learned that every row, table, etc in postgres can be associated
to a globally unique object id (oid), correct?  I tried to explore the system
tables, pg_, etc but I could not find a table which actually just contained the
oids, so I assume that this is hidden somewhere on a layer below the
database...  I want to know what the best method to implement this system will
be...  I am thinking triggers / store procedures?  but where do I store them...
on each table that may have a dependency?

any advice would be appreciated...
later,
Andy