Hierarchy of tables - Design problem

[Martin Moreno]

Hi all experts,

I've been fighting against this problem for a while but somehow I can't find a solution.

I have three tables:

ENGINE
GENSET
GENSET_UNIT

An ENGINE can be used in one or many GENSET, but a GENSET has always an ENGINE.
Similarly, a GENSET can be used in one or many GENSET_UNIT, but a GENSET_UNIT has always one GENSET. This structure is very stable (that's why I decided to use a hierarchy of tables).

So far so good. Now I have to model the parts explosion for GENSET_UNIT (since that is the product my company sells). There are parts which are used to build an ENGINE, other to build a GENSET and other to build the GENSET_UNIT-
Since I don't want to repeat the linking of parts that are needed to build an ENGINE for all GENSET_UNIT, I was expecting to be able to define for each table (ENGINE, GENSET, GENSET_UNIT) which parts are needed.
I'd have then 3 tables linked somehow to the table PART.

This doen't look that good, I reckon.

Could possibly someone tell me wheter I am doing wrong and what would be the best approach for my problem?

Thank you very much!!