Composite datatypes, dynamic member fields

Hello, 

I'm planning to build some kind of simple object oriented database and
came across PostgreSQL because of it's nearly unlimited ways of
extensibility.
The documentation is really good an I learned a lot about composite
datatypes, how to program them in c, create indices ... from the "Server
Programming" section of the "Developer Manual".
The problem in my case is that I don't know the names of the attributes
beforehand so I can't do a table bases mapping with one table for each
type of object ("class"). So I thought It would maybe be possible to
store the objects always in the same composed datatype - with "dynamic
member fields".
Ok this may be completely insane but ...

Maybe you could just tell me if it's worth to dig deeper.

Robert Staudinger