MDM Inheritence question

Dear MDM Specialists,

We are in SP03 and we have a need in which there might be a structure like

A

B

C

Now we might have a field called description that need to exist in all the 3 levels.We want the description from level "A" to flow to the description in level B.Then at Level B we may choose to override or append that info.

What is the best way to accomplish this.

Thanks.

Hari