public void clearTypes() {
    // leave it to OREResource to handle type clearance
    super.clearTypes();

    // ensure that the required type is still set
    res.addProperty(RDF.type, ORE.Aggregation);
  }
  public void setTypes(List<URI> types) {
    super.setTypes(types);

    // ensure that the required type is still set
    Selector selector = new SimpleSelector(res, RDF.type, ORE.Aggregation);
    StmtIterator itr = model.listStatements(selector);
    if (!itr.hasNext()) {
      res.addProperty(RDF.type, ORE.Aggregation);
    }
  }