public void AddInRelation(IDesignRelation ir)
 {
     if (!InRelationList.Contains(ir))
     {
         InRelationList.Add(ir);
     }
 }
 public void RemoveRelation(IDesignRelation dr)
 {
     if (OutRelationList.Contains(dr))
     {
         OutRelationList.Remove(dr);
     }
     if (InRelationList.Contains(dr))
     {
         InRelationList.Remove(dr);
     }
 }