Relationship between a Document number, Class and Class type

Hi All,

I'm trying to fetch all the doument numbers based on

Material Number (Object Key),

Class, and

Class Type.

I'm able to relate the Material number and Document number through DRAD table.

Could any one tell me in which way the Document number is related to the Class and Class type, and the corresponding tables which gives the relation?

Lots of thanks in advance,

Saravanan Rajan