Basics of IDoc...

An IDoc (intermediate document) is a standard data structure for electronic data interchange (EDI). IDocs are used for the data interchange between SAP systems as well as between an SAP system and an external system. IDocs serve as the vehicle for data transfer in SAP's Application Link Enabling (ALE) system. The contents, structure, sender, receiver, and current status of the IDoc are defined in the IDoc header.Data acquisition from an SAP source system is a very common scenario in SAP BW. This process involves extracting the data using either standard business content-provided extractors or custom-built extractors.
Failure of data to load usually leads to loss of productive time in re-triggering the extraction. For the scenario that we cover in this article, a data load failure leads to restarting the mirror initialization process. Therefore, this article begins by explaining the process of communication between BW and the source system through IDocs and then applying this knowledge to recover a failed data load without having to restart the mirror initialization process.

Data extraction from an SAP R/3 source system to BW begins when BW sends a request in the form of a request IDoc. The source system then extracts the data and sends it to the BW system. During this activity of data transfer, the two systems exchange additional information from time to time in the form of info IDocs. These info IDocs also transfer the information about the extracted data, such as data source details, data package number, and number of records. Therefore, you should acquire a detailed understanding of the IDoc exchange process to help you more easily deal with problems such as failed requests.

Communication Between BW and R/3 During Extraction
When BW executes an InfoPackage for data extraction, the system sends a request IDoc (RSRQST) to the Application Link Enabler (ALE) inbox of the source system. This IDoc  contains information such as the request ID (REQUEST), request date (REQDATE), request time (REQTIME), Info-Source (ISOURCE), and update mode (UPDMODE). The source system acknowledges the receipt of this IDoc by sending an info IDoc (RSINFO) back to the BW system. The status is 0 if it is OK or 5 for a failure.

Once the source system receives the request IDoc successfully, it processes it according to the information in the request. This request starts the extraction process in the source system (typically a batch job with a naming convention that begins with BI_REQ).

The request IDoc status now becomes 53 (application document posted). This status means the system cannot process the IDoc further.

The source system confirms the start of the extraction job by the source system to BW by sending another info IDoc (RSINFO) with status = 1 Transactional Remote Function Calls (tRFCs) extract and transfer the data to BW in data packages. Another info IDoc (RSINFO) with status = 2 sends information to BW about the data package number and number of records transferred

At the conclusion of the data extraction process (i.e., when all the data records are extracted and transferred to BW), an info IDoc (RSINFO) with status = 9 is sent to BW, which confirms the extraction process.

 Note:

If no data is found in the source system for extraction, an info IDoc (RSINFO) communicates this to the BW system with status = 8.
Below are few Idoc Status Number:

0		Not used, only R/2
1		IDoc generated
2		Error passing data to port
3		Data passed to port OK
4		Error within control information of EDI subsystem
5		Error During Translation
6		Translation OK
7		Error during syntax check
8		Syntax check OK
9		Error during interchange handling
10		Interchange handling OK
11		Error during dispatch
12		Dispatch OK
13		Retransmission OK
14		Interchange Acknowledgement positive
15		Interchange Acknowledgement negative
16		Functional Acknowledgement positive
17		Functional Acknowledgement negative
18		Triggering EDI subsystem OK
19		Data transfer for test OK
20		Error triggering EDI subsystem
21		Error passing data for test
22		Dispatch OK, acknowledgement still due
23		Error during retransmission
24		Control information of EDI subsystem OK
25		Processing despite syntax error (outbound)
26		Error during syntax check of IDoc (outbound)
27		Error in dispatch level (ALE service)
28		IDoc sent to ALE distribution unit retroactively
29		Error in ALE service
30		IDoc ready for dispatch (ALE service)
31		Error - no further processing
32		IDoc was edited
33		Original of an IDoc which was edited
34		Error in control record of IDoc
35		IDoc reloaded from archive
36		Electronic signature not performed (timeout)
37		IDoc added incorrectly
38		IDoc archived
39		IDoc is in the target system (ALE service)
40		Application document not created in target system
41		Application document created in target system
42		IDoc was created by test transaction
50		IDoc added
51		Application document not posted
52		Application document not fully posted
53		Application document posted
54		Error during formal application check
55		Formal application check OK
56		IDoc with errors added
57		Test IDoc: Error during application check
58		IDoc copy from R/2 connection
59		Not used
60		Error during syntax check of IDoc (inbound)
61		Processing despite syntax error (inbound)
62		IDoc passed to application
63		Error passing IDoc to application
64		IDoc ready to be transferred to application
65		Error in ALE service
66		IDoc is waiting for predecessor IDoc (serialization)
67		Not used
68		Error - no further processing
69		IDoc was edited
70		Original of an IDoc which was edited
71		IDoc reloaded from archive
72		Not used, only R/2
73		IDoc archived
74		IDoc was created by test transaction
75		IDoc is in inbound queue