system tables

Hi,

I've spent several hours browsing the system tables and the online
documentation about them but I still can't find how to extract
following information:

1. How do I find the user name for a given pid?

2. Where's the list that links all valid text encoding names with the
numbers representing them?  (E.g. UNICODE = 6)

Is there an easy way to recoup how the different system tables are
related to each other, or does one simply have to know?

Thanks,

Marc