POSNR - The misleading field in ECC

I was building a DSO the other day and was wondering how to list the key fields and data fields..I was using 2 data sources 2LIS_11_VASTH and 2LIS_11_VASTI and was pulling in data to 2 different datasources and was wondering what info objects should fill in the key fields and data fields. now these 2 data sources come from tables VBUK and VBUP..and in general the key fields for a data source are generally the key fields in the backend ECC tables and i decided to mention the VBELN (0DOC_NUMBER)and POSNR (0DELIV_ITEM)as my key fields for the DSO !

the way i identify fields in ECC and relate them to BI is using this table RSOSFIELDMAP in BI and also table RSRTFIELDSH in ECC....i decided to have 0DELIV_ITEM as the key field since the table VBUP has the key fields POSNR and the corresponding field in RSOSFIELDMAP is 0DELIV_ITEM .....HOW MISLEADING !!

If you look at the various SD tables, VBELN and POSNR are commonly used as the document number and document line item. For VBAP and VBUP, it's referring to the Sales Order Line Item with the columns VBELN and POSNR as the key for both tables. However, if you look at the LIPS table, which is the Delivery Line Item table, it too has VBELN and POSNR as the key. Likewise, the VTTP table, which is the Shipment Line Item table, also has VBELN and POSNR as the key.....the moral of the story for BI folks is to use the table RSOSFIELDMAP with caution and speculation ....POSNR is indeed a mileading field...I just prooved my point here SAP !!