Nested Table in PostgreSQL or some alternative Variants

Hello there

I've a problem. I can't find some information about nested tables in 
PostgreSQL. Is this Features possible in pgsql or not?

* When yes, how i can use and create nested tables with pgsql?
* When no, which alternative are there (for same problem definition)?

Thank you for help.
Greetings from Zurich, Switzerland.
Thomas Zuberbuehler