public StructuredRetrieval(StructuredIndex index, Parameters factoryParameters) {
   this.index = index;
   Parameters featureParameters = factoryParameters.clone();
   featureParameters.add("collectionLength", Long.toString(index.getCollectionLength()));
   featureParameters.add("documentCount", Long.toString(index.getDocumentCount()));
   featureFactory = new FeatureFactory(featureParameters);
 }