System catalog diagram

Hi,

does anybody have a complete diagram showing the system catalog tables
with their attributes and associations ?
I could only find one for the major system catalogs at
http://www.ninthwonder.com/info/postgres/programmer/extend289.htm .

I find it difficult to find out which pg table holds the information I
need reading through the pg documentation. For instance I currently need
to get the OID for a given namespace in order to query the pg_type
table, and I don't know where to find that information...

Regards,

--
Samuel Thoraval