indexing mutiple table

[Radha C.]

Hi,
 
I am trying to index different tables with different primary keys and
different fields.
 
Table A - primary field is a_id
Table B - primary fiedls is b_id
 
How to specify two different primary keys for two different tables in
schema.xml?
 
Is it possible to create a data-config with different root
entities/documents and index/search everything?
 
Thanks in advance.