BDC , LSMW, Conversions faq in abap

1. What is BDC ?
   
2. What is call transaction method ? what is the
   syntax/procedure?
   
3. What is session method and what is the
   syntax/procedure?
   
4. Difference between call transaction & session method?
   
5. which of these methods can be best used in background
   process?
   
6. What is direct input method?
   
7. How LSMW is advantageous than normal BDC?
   
8. what are the steps in lsmw?
   
9. IN LSMW can you use BAPI, ?
   
10. Can you call a bdc from a report program?
    
11. what is the difference between synchronus &
    asynchronus methods?
    
12. call transaction uses synchronus or synchronus method?
    
13. session method uses synchronus or synchronus method?
    
14. What is bapi?
    
15. how bapi is different from call transaction/session?
    
16. what r the advantages of bapi?
    
17. for uploading master data(ex:customer data) into sap,
    which methods you prefer? call
    transaction/session/lsmw/bapi? why?
    
18. tell any 2 standard bapi function modules used for
    uploading sales order data?