need advice.

I have a database that should be quite simple to do.

I have a base object that is easily defined
as

create table myObject (
a integer,
b integer,
len integer,
data bytea
);

Now this really should be a type:
And oddly enough it is the only type of data in the entire database.

A list of these is a row in a table.
The list size is variable.

level a one to many level b
level b one to many level c
level c one to many level d

Each of these levels is a list (or row) of these objects..

What does the scheme or sql of this look like.
I'm sort of new to databases.. but I don't know how to make the 'entity
relationships' between the levels.

Help?