Object table: classification extraction?

hello experts,

i am trying to extract classification data for materials in the material master.

When i try to create a datasource for the same in the transaction CTBW, it asks me for a object table. What is this? how do i know the correct object table from the displayed list?

there are different class types, classes and characteristics for each class. Do i need to create a different datasource for each class type?

how to link the transaction data to these characteristics in BW? i.e for eg: how to have these captured from sales order transaction in R/3?

Detailed answers will definately will rewarded...

thanks a lot in advance.