Multiples schemas

Hi,
Is there a way to construct a multi schema in my data base?
Something like:
mysystem.finances.money.tables
mysystem.finances.money.functions
mysystem.finances.credits.tables
mysystem.finances.credits.functions
mysystem.amount.products......
....

Or can I use another database like:
createdb DB1
createdb DB2
psql DB1
select * from DB2.schema.table

Or i need to construct the tables in the same database and the same schema like:
mysystemdb.amount.products
mysystemdb.amount.vendors
mysystemdb.amount.clients
mysystemdb.finances.money
....

Could I create a multi schema into another schema ??? or is there only one level
for schema sctructs?

Thanks for all