Oracle Database Discussions

Hi,

I have to support one database where is quite a lot tables and relations.
can you please advise me a tool which help me to get database structure (UML).
I would get diagram where will be schemas, tables and relationship between tables, primary keys, foreign keys.
I think that this process called "reverse engineering"
Is there any tool which help me?
I suppose that I connect to db via tnsnames as sys so I'll see all objects.

Thank you for help.
Regards,
Tom