Broadly speaking, a CV can range from a short list of clearly defined, mutually exclusive, and exhaustive terms, which are the only choices for usage in a specific context (e.g., populating certain DDI elements or attributes) through a classification to something as complex as a thesaurus with thousands of terms and term relationships. A CV has also been described as "A set of subject terms, and rules for their use in assigning terms to materials for indexing and retrieval." (http://www.cs.cornell.edu/wya/diglib/MS1999/Glossary.html). In a CV, a term consists of one or more words used to represent a concept (example: “fear”; “females”; “child care”). Terms are selected from natural language for inclusion in a controlled vocabulary.