SPAU and SPDD

When you apply a package, a large number  of objects are changed.
If you have applied any OSS notes to objects in your system, the hot package may overwrite these objects.  
SPDD is used to identify dictionary objects  

and

SPAU (repository objects), will identify any objects where the hot package is overwriting changes you have made through OSS notes.  
You must check all objects identified in SPAU and decide whether you need to reapply the OSS note or reset the code to the original SAP Code.  
If, for instance, you are applying hot package 34, SPAU identifies an object where you have applied an OSS note.  You must check the OSSs note and see if SAP have fixed that note in a hot package.  
If the OSS note has been fixed in hot package 34, then you should reset the object to its original source code.  This means that there is no repair flag set against this object again and it is now SAP standard code.  
If, however, the object is not fixed until hot package 38, or there is no fix available you have to reapply the OSS note, otherwise users will encounter the problems they had before the note was applied.
You must transport all reapplied notes and Reset to SAP Standard objects after you apply your hot package to your QAS and PRD systems.