Terminology

A guide to the jargon of controlled vocabularies, in the context of applying the e-GMS

How to make it easier for people to find information through the electronic networks? Only part of the answer is to provide good hardware and software. Equally important is to label each item of information carefully before it gets into the system, and this is the role of metadata .

The e-Government Metadata Standard ( e-GMS ) sets out the rules for labelling items of information. It tells you to give each item a name, a date, etc. It explains how to use these elements, and sometimes it asks you to apply an encoding scheme, with very precise rules for particular elements. For example, the encoding scheme for Date tells you to write 6th May 2005 as 2005-05-06 and not 2005-06-05 nor 6/5/05 nor 6.v.2005 nor May 6 05 nor any of the other variants. The idea is to avoid ambiguity and promote efficiency.

A controlled vocabulary is an encoding scheme that gives a finite list of all the terms available for use with a particular element of the metadata. For example, the e-GMS controlled vocabulary for describing Audience is a list of 19 terms, such as Carers and Children. The purpose of the Audience encoding scheme is to help you label items of information with key categories of people for whom they are specifically intended.

Labelling is especially difficult when you try to describe the Subject of an item, i.e. what it is about. There are usually many different ways of saying the same thing. A controlled vocabulary is needed so that the people doing the labelling use the same terms as the people searching, for describing the same concept. Here are some descriptions of various types of controlled vocabulary, starting with the simplest:

.  Authority list : a list of terms for use in naming particular entities consistently, for example, a list of names of people or of organisations

.  Classification scheme : a scheme that groups like things together and separates unlike things. The groups are arranged in a logical sequence, often in hierarchies. Sometimes each group is represented by a code or notation. Classification schemes are very commonly used in libraries.

.  Thesaurus : a controlled vocabulary that provides many links between terms to help with finding the right one. As well as the terms allowed for labelling purposes, the thesaurus has other entry points from synonyms of the terms. A thesaurus should comply with the British Standard BS 8723 or the international standard ISO 2788. It is important to understand that the word "thesaurus" in everyday use refers to something different - not a controlled vocabulary and not usually compliant with ISO 2788 .

.  Taxonomy : a classification scheme designed for use with electronic media. Usually it supports navigation in websites and portals, and sometimes it also helps with keyword searching. Usually it has a strong hierarchical presentation, and sometimes it has features common in a thesaurus, such as term linkages and entry points through synonyms. Biologists give a slightly different meaning to the word "taxonomy", referring specifically to a hierarchical classification of organisms.

.  Ontology : a scheme that specifies concepts and the relationships between them, for purposes of communication between computers. Typically ontologies are structured to support making inferences, but they may also be considered as controlled vocabularies Ontologies tend to work best in well defined domains. The word "ontology" is often used much more loosely that this, to apply to a wide variety of vocabularies. Before the advent of computers, its original meaning was, "the science or study of being" .

The words above were chosen as working definitions, fully compatible with BS 8723 "Structured Vocabularies for Information Retrieval - Guide". The Glossary of terms relating to thesauri and other forms of structured vocabulary for information retrieval has a much longer list, with d efinitions that are more academically correct.

Other useful links:

Metadata? Thesauri? Taxonomies? Topic Maps! Making sense of it all

What are the differences between a vocabulary, a taxonomy, a thesaurus, an ontology, and a meta-model?

Stella Dextre Clarke

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