During the Recording of BDC using SHDB these OK codes are automatically recorded in the code
Or you can use your own 4 letter function codes as OK codes
see the doc
In your ABAP programs, you should work with the OK_CODE field instead of SY-UCOMM. There are two reasons for this: Firstly, the ABAP program has full control over fields declared within it, and secondly, you should never change the value of an ABAP system field. However, you should also always initialize the OK_CODE field in an ABAP program for the following reason:
In the same way that the OK_CODE field in the ABAP program and the system field SY-UCOMM receive the contents of the corresponding screen fields in the PAI event, their contents are also assigned to the OK_CODE screen field and system field SYST-UCOMM in the PBO event. Therefore, you must clear the OK_CODE field in the ABAP program to ensure that the function code of a screen is not already filled in the PBO event with an unwanted value. This is particularly important when the next PAI event can be triggered with an empty function code (for example, using ENTER). Empty function codes do not affect SY-UCOMM or the OK_CODE field, and consequently, the old field contents are transported.
In your application programs, the first step in PAI processing should be to save the function code in an auxiliary variable and then initialize the OK_CODE field. You can then read the function code from the auxiliary variable (for example, using a CASE structure), and control the program flow from there.
The OK_CODE field can have a different name on each screen. However, common practice is to use the same name for the field on each screen of an ABAP program. You then only need one field in the ABAP program, with the same name, into which the function code is placed, and from which you can read it.
Refer the link:
http://help.sap.com/saphelp_47x200/helpdata/en/d1/801e61454211d189710000e8322d00/frameset.htm
Bluesky
