Hi Anni,
I am not sure which DDL you want to check. if you want to check the source code of these DDLs in S4HANA On Premise.
You need
1. run program vdm_metadata in SE38 in S4HANA OP
2. check the package name and DDL name
3. open the HANA studio with Eclips for ABAP
4. Logon the S4HANA OP system with user access
5. Find the DDL in the package
And then you could check the source code.
if you are talking about the S4HANA cloud version, I don't think there is a way to check the source code of DDLs.
Hope it help.
regards
Ned