IDOC Information

IDoc (for intermediate document) is a standard data structure for electronic data interchange (EDI) between application programs written for the popular SAP business system or between an SAP application and an external program. IDocs serve as the vehicle for data transfer in SAP's Application Link Enabling (ALE) system. 

IDocs are used for asynchronous transactions:  Each IDoc generated exists as a self-contained text file that can then be transmitted to the requesting workstation without connecting to the central database. 

Another SAP mechanism, the Business Application Programming Interface (BAPI) is used for synchronous transactions. 
A large enterprise's networked computing environment is likely to connect many geographically distributed computers to the main database. These computers are likely to use different hardware and/or operating system platforms. An IDoc encapsulates data so that it can be exchanged between different systems without conversion from one format to another. 

IDoc types define different categories of data, such as purchase orders or invoices, which may then be broken down into more specific categories called message types. Greater specificity means that an IDoc type is capable of storing only the data required for a particular transaction, which increases efficiency and decreases resource demands. 

An IDoc can be generated at any point in a transaction process. For example, during a shipping transaction process, an IDoc may be generated that includes the data fields required to print a shipping manifest. After a user performs an SAP transaction, one or more IDocs are generated in the sending database and passed to the ALE communication layer. The communication
layer performs a Remote Function Call (RFC), using the port definition and RFC destination specified by the customer model. 

The IDoc is transmitted to the receiver, which may be an R/3, R/2, or some external system.      

What are the main advantages of IDOC?

IDoc is the data Format used by the SAP in data transfer using ALE /EDI methods. They provide more data security.  An IDoc is an intermediate document used to send data in two ways, that is internal and the external point for you.

In BW, IDoc is a transfer mode, when you create a Infosource you can select the transfer mode as PSA or IDOC. Its the method provided for backward compatibility. In older version the hierarchies where loaded using IDOC transfer method. Now its possible with PSA but still that method is available to load the hierarchies.

An example in SD:
For creating sales documents (sales order) through IDOCS you will have to use the T code WE19.  In that click basic type and enter order05(IDOC type) and select via message type then enter ORDERS(message type), click execute.

You will get to see many fields. here you have to enter the data that you enter in the VA01 screen in order to create sales order. The data such as material name, date, qty, P.O no etc.  After entering all the data, you click standard inbound the IDOC would be created by the system. You can see the created order by going in to VA03 screen.

Next time when you create the IDOC, in same tcode WE19 screen, click existing IDOC and enter the IDOC which you created in the above step and just change the P.O no. System will create new sales order through new IDOC

Before doing all you need to maintain the partner profile in T code WE20