TaxonomyWriter taxoWriter = new DirectoryTaxonomyWriter(taxoDir);
EnhancementsDocumentBuilder builder = new EnhancementsDocumentBuilder(
taxoWriter, new DefaultEnhancementsIndexingParams(
new AssociationEnhancement()));
// index documents, 50% have only 'b' and all have 'a'
for (int i = 0; i < 100; i++) {
Document doc = new Document();
CategoryContainer container = new CategoryContainer();