Regarding Direct Input Methods In SAP

Hi All,

Can anybody answer my questions below.

1. What is meant by direct input method!

2. What is the basic diffrence between direct input method & other two BDC methods [CALL TRAN & SESSION].

3. What are the diffrent direct input methods available in SAP. How can we find Direct input methods for certain scenario's like Material Master/Customer master, Sales order, Invoice etc...

Thanks in advance.

Thanks & Regards,

Rayeez.