A classification scheme used to index data. Stratifyd uses faceted hierarchical taxonomies with controlled vocabularies; labels are broad or narrow branches of the hierarchical categorization tree. The controlled vocabulary for each label is simply a restricted list of words and Boolean logic meant to index documents.
Documents are funneled into labels based on a purely disjointed "did match" or "did not match" one of the terms in the label's controlled vocabulary. Narrower labels work with their broader parent labels vocabularies as nested levels of match logic, enabling a more fine-grained classification model.
Ontologies take this a step further by classifying, showing the properties of, and outlining the relationships between concepts or categories in an parent domain.