Data Modelling in BI

please help me on this to be clear and firm up the data model in BI 7.0.please answer step by step eg 1,2 3,

1. I am trying to load the two purchasing cube 0pur_c01 and 0pur_c02 from the data sources scheline 2lis_02_scl and 2lis_02_ITM and 2lis_02_hdr

2. Now question is that i see confusion here to load and design the data model. please tell how

option 1. create transformation from data source 2lis_02_scl to infosource 2lis_02_scl and then create the transformation from infosource 2lis_02_scl to cube 0pur_c01 and the repeat same thing for other data source

now create IP from DS to load PSA and create the DTP to load the from DS to CUBE

3. nOW I SEE peoploe making transfer structure for IS 2lis_02_scl AND connect to DS 2lis_02_scl and then going to cube and creating UR from IS 2lis_02_scl TO CUBE like in 3.5 WHY THis is needed now in BI 7.0??? if we are going by transformation FROM DS TO IS AND IS TO CUBE AND THEN DO THE DTP

Please clarify the right approach to solve the requiremnt

4. i also see the way suggested by sap http://help.sap.com/saphelp_nw04s/helpdata/en/44/0243dd8ae1603ae10000000a1553f6/content.htm

to make 2 transform from IS To IS in case 3 why this is required since sap provided different IS

5. why not create the DS TO IS transform for each ds such as 2lis_02_scl , 2lis_02_itm and DTP to cube seperately for each DS.

please help

thanks

soniya kapoor