code: static public UpdateSpecifier computeUpdateSpecifier(
  			Document sourceDoc
  			,JSONObject targetDoc
  			) throws Exception {
  		
  		DigestComputerSha1 digestComputer = new DigestComputerSha1();
  		DocumentDigest dd = digestComputer.computeDocumentDigest(sourceDoc);
  		
  		return computeUpdateSpecifier(
  				sourceDoc
  				,dd
  				,targetDoc
  				,DocumentUpdateProcess.Schedule.UPDATE_UNLESS_MODIFIED
  				,UpdateObjectComparator.getNunaliitComparator()
  				);
  	}
docs: Returns the actions required during a document update to modify
  a target document so that it become equal to a source document.
  @param sourceDoc Source document
  @param targetDoc Document currently on the target location
  @return Specifier that explains what needs to happen during an update
  @throws Exception