Hello Al
Maybe in your workflow, before generating the instance, you can do a select on table DRAW to get the TYPE (DOKAR)....IF you are sure that the Drawing Number (DOKNR) will NOT be common across various types (since DOKNR is just a partial key of that table).
Once you have the TYPE, you can create an instance of the object DRAW (using the same way as you are currently doing) and pass the key as a concatenation of DOKAR (Type) , DOKNR (Number), DOKVR(version) , DOKTL (Part).
regards,
Modak