Can I use different format (schema.xml) for a document (like car document)?
So that I can use different index to query the same class of documents differently?
(OK.. I can use two instances of Solr, but.. that's the only way? )
Only one schema is possible for a Core.
You can always have different Cores within the same solr with the Multicore configuration.
However, if you have the same entity and want to query it differently, you can have the same schema.xml to hold the values different fields and different field types (Check copyfield) and have different query handler to have weighted queries depending upon the needs.