code: static public String getDocumentIdentifierFromSubmission(JSONObject submissionDoc) throws Exception {
  		JSONObject submissionInfo = submissionDoc.getJSONObject("nunaliit_submission");
  		JSONObject originalReserved = submissionInfo.optJSONObject("original_reserved");
  		JSONObject submittedReserved = submissionInfo.optJSONObject("submitted_reserved");
  
  		// Get document id and revision
  		String docId = null;
  		if( null != originalReserved ){
  			docId = originalReserved.optString("id");
  		}
  		if( null == docId && null != submittedReserved){
  			docId = submittedReserved.optString("id");
  		}
  		
  		return docId;
  	}
docs: Computes the target document identifier for this submission. Returns null
  if it can not be found.
  @param submissionDoc Submission document from the submission database
  @return Document identifier for the submitted document