Transfer Rules: How does the mapping work?

Question

Transfer Rules: How does the mapping work?
Is there a document out there that explains the following or can someone help clarify it for me. I have some confusion on what is really going on.
When I create an InfoSource (IS_Test)  as a “Flexible update…”  and then “Assign DataSource”  (DS_Test) and I respond Yes, to the message “DataSource assignment DS_Test to InfoSource IS_Test Save”
a) <b>Under “Transfer_Structure/Transfer_Rules”</b> in the InfoSource
1)  the “Transfer Rules” tab, what are the fields found in the right column (Assigned InfObjct-field)? And where do the fields you enter in the left column (<b>Communication Str/</b>Transfer rules) eventually go?
2)  the “DataSource /Trans. Structure” tab, can I always assume that all the fields in the right column (DataSource) came from DS_Test? The left column (Transfer Structure), in my test was exactly the same as on the right. Where do these fields eventually go?
b) Under “<b>Communication_Struct.”,</b> in the InfoSource
3. the right column (ISource Fileds) where from those InfoObjects. if I am now creating my InfoSource. Where did they come from?
4. The left column is “<b>Communication Structure</b>”, which at this point has no InfoObjects, if I move a couple of InfoObjects from the right to the left, where do these Objects in the left eventually go?
5. what is the relationship between the “Communication Structure” in 4 and 1? Or any relationship between a) and b) as a whole?
Thanks.

Answer 1

Hi Caud,
As Ashish pointed out, communication structure contains fields (infoobjects) that suppose to go to data targets. Which IO in CS to which IO in the data target will go (and what transformation of data may occur) is determined in URs of the data target.
The transfer structure is the structure in which the data is transported from the source system into BW:
http://help.sap.com/saphelp_bw33/helpdata/en/3f/0e503c3c0d563de10000000a114084/frameset.htm
In “Transfer_Structure/Transfer_Rules” in the IS, DataSource /Trans. Structure” tab, right part shows fields in the Datasource, the left part – fields in the transfer structure. There is also a transfer structure in R/3 for a given DS. Transfer structure in BW is created identical to the TS in R/3 during TRs activation.
During data load data are transferred 1:1 from TS in R/3 to TS in BW.
TS in BW corresponds to the PSA table structure.
How data from PSA are transferred to the CS is determined in TRs.   
The 3rd column (“Field”) (“Transfer Rules” tab, right part (Assigned InfObjct-field)), contains field names of the DS (TS); and the 1st column shows IO in the CS to which the DS field will go. So, it’s a mapping DS filed -> CS field.
The left part (“Communication str./Transfer rules”) is always identical to the CS content. But the 4th column (“Tp”) shows possible data transformation during transfer from PSA to CS. If this column contains a yellow triangle then there is no transformation (Value of DS field will go to value of CS field). If there is a red cross, it means that no data for this CS field is supplied from a DS. You can click on this yellow triangle and choose: 1). Another field from a DS; 2). Constant; 3). ABAP routine; 4). Formula. So, here you can determine the data transformation. Moreover, there is a possibility to create a start routine (blank sheet icon at the top).
And finally, here are the answers on your questions:
Q:
a)     Under “Transfer_Structure/Transfer_Rules” in the InfoSource
1) the “Transfer Rules” tab, what are the fields found in the right column (Assigned InfObjct-field)? And where do the fields you enter in the left column (Communication Str/Transfer rules) eventually go?
A: Right part shows a mapping between DS and CS fields. Left part shows CS fields and data transformation (TRs) during data transfer from TS (PSA) to the CS. These are fields in the CS that will go to data target and which are fed from a TS (DS).
Q: 2) the “DataSource /Trans. Structure” tab, can I always assume that all the fields in the right column (DataSource) came from DS_Test?
A: Yes, you are right.
Q: The left column (Transfer Structure), in my test was exactly the same as on the right. Where do these fields eventually go?
A: As I described, left and right parts are identical. These fields will go to CS.
Q: b) Under “Communication_Struct.”, in the InfoSource
3. the right column (ISource Fileds) where from those InfoObjects. if I am now creating my InfoSource. Where did they come from?
A: these are fields from an IS template, the name of this template you can see above this right part.  Actually, during IS (CS) creation you can choose different templates and choose fields from them transferring them into the left part.
Q: 4. The left column is “Communication Structure”, which at this point has no InfoObjects, if I move a couple of InfoObjects from the right to the left, where do these Objects in the left eventually go?
A: these are fields of CS (left part) and as I said before they will go to data target.
Q: 5. what is the relationship between the “Communication Structure” in 4 and 1? Or any relationship between a) and b) as a whole?
A: CS in 4 just shows IOs that will be transferred to data target. CS in 1 also shows how values for CS IOs are to be fed and transformed.
Best regards,
Eugene
Message was edited by: Eugene Khusainov