public static Timestream Create(string id, string name, string headId, string metadataId, string startTime, string endTime)
 {
     Timestream ts = FindFromId(id);
     if (ts == null) {
         ts = new Timestream(id, name, headId, metadataId, startTime, endTime);
     }
     return ts;
 }
 public TimestreamData(Timestream ts)
 {
     ts.timestreamDataList.Add(this);
     this.timestream = ts;
 }