Confussion with Table_lock levels and isolation levels.

Hi fellows !

I would only want to ask some questions concerning table-locking levels
and isolation levels:

     First of all:  should I assume that Access___ modes imply locking
the complete table and Row___ imply locking only the
     rows which have been accessed, and beyond that the conflicts will
be solved according the hierarchy between modes, or
     is this distinction inaccurate ?

     Second:
          What does exactly mean that a mode 'CONFLICTS'  with another ?

          Does it mean that another concurrent transactions having these
modes will have to wait until the first transaction
          have finished (commit or roll back) ?
          Can we determine (when accessing a row in a table) wether we
will have a conflict or not according to the criteria
          explained in the previous question (Access-> complete table,
Row -> rows accessed) ?

     Third:
          If all the previous assumptions are true:
               When there is a conflict, will the only consequence be
that all concurrent transactions will be processed in a
               FIFO serie and not in parallel ?
               What about all the concurrent transactions which haven't
conflicted ? How can you avoid falling into
               contradiction with the isolation level (and assure the
protection against non-repeteable reads or phantom
               reads ?
               I feel those two levels (transactions and isolation
levels) are two layers so the transactions will be
               processed according to a FIFO serie when exist any
problem concerning the isolation level or the
               table-locking. Is this a good way to describe the way
PostgreSQL manages the things ?

Thank you very much for your help.

Best regards and good Y2K,

Gabi     :-)