Page 174 - DLIS405_INFORMATION_STORAGE_AND_RETRIEVAL

Unit 14: ERIC and Thesaurofacet

the classification schedules and thesaurus. Each term appears both in the thesaurus and in the Notes
schedules.
In the schedules the term is displayed in the most appropriate facet and hierarchy: the thesaurus
supplements this information by indicating alternative hierarchies and other relationships which
cut across the classified arrangement. The thesaurus also controls word forms and synonyms and
acts as the alphabetical index to the class numbers.
The thesaurus is one of the most commonly used controlled vocabulary indexing tools - the aim of
the FACET project is to investigate the retrieval potential of thesauri. FACET investigates the closer
integration of the thesaurus into the interface and search techniques that do not require the user to
exactly match how an item has been indexed.
FACET collaborates with the J. Paul Getty Trust in exploring the retrieval potential of its vocabularies,
in particular the Art and Architecture Thesaurus (AAT), and with the National Museum of Science
and Industry (NMSI) in its attempts to promote wider access to its collections database. The aim is
to complement NMSI’s development of major areas of ‘rich content’. Railway/Locomotive History
has been selected as one area particularly appropriate for the project due to its AAT coverage and
synergy with ongoing work at the National Railway Museum on extending the AAT with railway
terms. The mda and CHIN act as advisors to the project.

What is a thesaurus and why FACET?

Thesauri and classifications are types of controlled indexing vocabulary, in which index terms are
restricted to a controlled set of terms. A large number of systems exist, covering a variety of subject
domains, for example the Medical Subject Headings, the Art and Architecture Thesaurus and the
Dewey Decimal Classification. These controlled vocabularies have long been part of standard
cataloguing practice in libraries and museums and are now being applied to digital hypertexts via
thematic keywords in metadata resource descriptors. Metadata sets for the WWW, such as Dublin
Core and the Resource Description Framework (RDF) typically include the more complex notion of
the Subject of a resource in addition to elements for Title, Creator, Date, etc.
It is recommended that, where possible, the Subject element be taken from a relevant controlled
vocabulary. This semantic index approach offers the potential for searcher and indexer to speak the
same language, and for a user to be guided to fruitful terms when searching a particular collection
for a particular purpose. Links between concepts in the subject domain can be expressed by the
semantic relationships in a thesaurus (or classification). The three main thesaurus relationships are
Equivalence (equivalent terms), Hierarchical (broader/narrower terms), and Associative (more
loosely Related Terms). Specialisations of the three main relationships offer possibilities for semantic
web applications.
Facet analysis is a key technique in thesaurus construction; concepts are decomposed into elemental
classes, or facets, which form homogenous mutually exclusive groups. The faceted approach to
subject analysis began in 1933 with Ranganathan’s Colon Classification (Personality, Matter, Energy,
Space and Time) and was subsequently elaborated by the British Classification Research Group.
Faceted thesauri or classification systems include MESH, BLISS, PRECIS and the main thesaurus
used in the project, the Art and Architecture Thesaurus (AAT).
The AAT is a large, evolving thesaurus (nearly 120,000 terms), organised into 7 facets (and 33
hierarchies as subdivisions) according to semantic role: Associated concepts, Physical attributes,
Styles and periods, Agents, Activities, Materials, Objects and optional facets for time and place.
Faceted thesauri are similar in structure to faceted classifications but explicitly represent equivalence,
hierarchical and associative links between concepts. A thesaurus can be used as a search thesaurus

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