System catalogues

Hi all

I have a problem which I'm not sure how to fix. I store my own metadata
about tables and databases in a central admin database. I would like to
combine data from the admin database with data from pg_attribute

for eg:
SELECT distinct a.attname FROM pg_class c, pg_attribute a, pg_type t WHERE
c.relkind = 'r' and c.relname = 'example' and a.attnum > 0 and
a.attrelid = c.oid and a.atttypid = t.oid ORDER BY attname

but where 'example' is a table in another database, not the admin
database. What I would like to do is a join on my admin metadata with the
data in pg_attribute to see where I have no metadata on the field in
question in the admin database. I hope that makes sense!

Is this possible? Has anyone written any sort of documentation on the
system catalogues that I might be able to read?

Thanks a lot guys

Cheers

Zak