controlled index

Controlled indexing is a method used in information science to organize and retrieve information. It involves assigning subject descriptors from a predefined list of authorized terms, often referred to as an authority list or a thesaurus. This controlled vocabulary helps users find relevant information by ensuring consistency in terminology. For example, a library might consistently use "Great Britain—Description and Travel" as a subject heading for all books on that topic, rather than using various synonyms like "travel in Britain" or "tourism in the UK".12

While controlled vocabulary systems are effective, they can be slow to adapt to new terms and evolving language. To address this, many information systems combine controlled indexing with free vocabulary, using abstracts and summaries written in ordinary language to supplement the subject headings. Machine indexing, a key component of this process, uses computers to analyze electronic text and assign these subject descriptors, creating an inverted index that links terms to their locations within documents.21