Difference between E1EDK01 and E1EDP01

Hey Guys

i m designing a mapping in XI for one of my business partner and am a little bit confused between E1EDK01 and E1EDP01 of ORDERS IDOC.

sometimes the business partner sends values in E1EDK01 and other times he sends under E1EDP01(due to which we get issues in mapping),i did check WE60 in R/3 but am unable to find a difference between the two fields

can you guys please tell me as per the business perspective whats the difference between E1EDK01 and E1EDP01,i mean under what condition we should get values in E1EDK01 or E1EDP01

Thanx

Saif