Best practices for structuring a thesaurus

[version française]


Documentary languages

Domcumentary languages are controlled or standardized vocabularies, whose purpose is to respond to the equivocation of natural language and the problems posed by polysemy and homonymy. They are used to index and describe the cntent of a resource and are intended to improve documentary research.

There are three main types of document languages: classification schemes, authority or subject heading list and thesauri. Classifications, such as the Dewey Decimal Classification, propose a hierarchical organization of concepts. Authority lists or headings are standardized terms that must be used in cataloguing or indexing to describe the content of documents. We can cite Rameau (Répertoire d’autorité-matière encyclopédique et alphabétique unifié), the subject indexing language used by the Bibliothèque nationale de France. Finally, a thesaurus structures a controlled vocabulary by describing the set of semantic relations that link concepts.

The use of controlled vocabularies is a recommendation of the Agence Nationale de la Recherche for the evaluation of data quality in data management plans. Similary, according to the FAIR principles, ‘to be FAIR, data must be described using a controlled vocabulary that is itself FAIR compliant. It must be easy to find with a persistent and unique identifier, documented and machine-readable.

The structure of a thesaurus

The construction of a thesaurus follows ISO standards (ISO 25964-1:2011 and ISO 25964-2:2013).

The ISO 25964 standard distinguishes between concepts, as a ‘mental representation’, and terms, as a linguistic expression of a concept in a given language.

A concept is expressed by a preferred or descriptor term and non-descriptor terms. It has hierarchical and associative relationships with other concepts. It is aligned with concepts in other thesauri through equivalence relationships. It can be defined and documented by differents types of notes.

  • Equivalence relationships between the preferred term and its synonyms

– The preferred term

In a knowledge organization system, the preferred (or retained, preferred) term is used to refer unambiguously to a concept. It is the descriptor of an indexing and the label appears in the display.

⚠ A thesaurus allows only one descriptor term per concept and per language.

⚠ The same descriptor term cannot designate several concepts. In case of homonymy, the scope of the term should be disambiguated by adding a qualifier in parenthesis:

Wood

Wood (zoology)

⚠ A single term cannot be both a descriptor and a non-descriptor.

– Synonyms

The descriptor term and the non-descriptor (or rejected, or non-preferred) terms that represent the same concept are related to each other by an equivalence relationship. It allows the control of synonyms and access to information.

According to the standards for constructing a thesaurus, are considered synonyms:

♦ Full names and abbreviations or acronyms: magnetic resonance imaging | IRM

♦ Common names and scientific names: spiders | Araneae

♦ Scientific and brand names: paracetamol | Efferalgan

♦ Terms of different linguistic origins: polychrome | multicolor

♦ Spelling variations: teacher | schoolmaster

♦ Ancient and modern appelations: $ exemple en anglais

Equivalence relationships also include quasi-synonyms. These are terms that are too specific to all appears as descriptors according to the domain addressed by the thesaurus.

Vegetarianism

UF : lacto-ovo vegetarian, lacto-vegetarian, ovo-vegetarian, semi-vegetarian, vegetarian.

Equivalence relationship can also include antonyms when they represent two aspects of the same concept, e.g. Literacy and Illiteracy.

  • Hierarchical relationships

A hierarchical (or generic-specific or parent-child or broader-narrower) relationship must link, from the most general to the most precise, concepts of the same category: entities, activities, agents, actions, properties.

For example, the terms Museums (entities), Curators (agents) and Museography (action) do not belong to the same categories and therfore cannot be in a hierarchical relationship.

The ‘some/all’ test allows to check the validity of the hierarchical relationship:

“Some/all” test

General hierachical relationships can be subdivided into three categories:

– The generic relationship

Modeled after the genus-species relationship, the concept represented by the specific term is a particular type or species of the concept represented by the generic term.

TGG Felidae
NTG Cats
NTG Lynx
NTG Panthera
NTG Puma

– The partitive relationship

The hierarchical all-part relationship concernes:

Body systems and organs
BTP Digestive system
NTP Liver
NTP Pancreas

Geographic locations
BTP Canada
PST Ontario
Ottawa PST
NTP Toronto

Disciplines and their specialties
BTP Medicine
NTP Cardiology
NTP Surgery
NTP Dermatology

Hierarchical organizations
BTP Corps
NTP Divisions
NTP Brigades
NTP Regiments
NTP Battalions

– The instance relationship

This relation characterizes the link between a category or class designated by a common name and an instance of this category, represented by a proper name.

BTI Mountains
NTI Alps
NTI Pyrenees

  • Polyhierarchy

Each concept can be linked to several other concepts by hierarchical relationships.

BT Musical instruments
TS Keyboard instruments
TS Piano
TS String instruments
TS Stringed Instruments
TS Piano

BT Visual object
NT Geometric pattern
NT Cruciform geometric pattern
NT Ankh
BT Symbolic objects
NT Symbol
NT Ankh

  • Top Term

A Top Term is the preferred term that represents the highest level concept in the hierarchy to which it belongs. It is therefore located at the ‘root’ of the vocabulary and constitues an entry point into one of the branches of a thesaurus.

  • Associative relationships

Associative relationships allow concepts that are not hierarchically linked but semantically linked to be brought together. To associate two concepts, the norm is that one must be a necessary element for the definition ot the other. For example,the concept of ‘Water supply’ is necessary for the definition of the definition of the concept of ‘pit’.

The associative relationships are reprocical. They make it possible to describe:

– Cause and effect:

Infections
NT Infectious diseases

– A whole and its part:

Books
NT Binding

– An action and an agent or instrument:

Gardening
NT Gardeners

– An action and the production of that action:

Publishing
NT Books

– An action and the object that undergoes that action:

Data Analysis
NT Data

– An action and the location of that action:

Primary Education
NT Primary schools

– A science and its object:

Paleontology
NT Fossils

– An object or action and its property:

Poisons
NT Toxicity

– An object or action and its role or purpose:

Tanks
NT Water storage

– A raw material and its product:

Skins
NT Leather

– A process and its neutralizing agent:

Inflammation
NT Anti-inflammatories

– An object and its origin:

Pit
NT Groundwater

– An object or concept and a unit or mechanism of measurement:

Temperature
NT Thermometer

– A profession and the person who practives that profession:

Masonry
NT Masons

Associative relationships also allow for the accosiation of ‘brother’ concepts that share the same generic term and overlapping meanings (ships and boats), contrary concepts (marriage and divorce), and complementary concepts (teaching and learning).

⚠ Two concepts cannot be linked by both hierarchical and associative relationships.

Type of relationshipsDirection of the relationshipFrench terminologyAbreviationsEnglish terminologyAbreviations
Equivalence relationship⇒ from descriptor to non-descriptorEmployé pourEPUsed forUF
Êquivalence relationship⇒ from non-descriptor to descriptorEmployerE ou EMUse 
Hierarchical relationship⇒ from specific term to generic termTerme génériqueTGBroader TermBT
Hierarchical relationship⇒ from generic term to specific termTerme spécifiqueTSNarrower Term NT
Hierarchical generic relationship⇒ from specific term to generic termTerme générique (générique)TGGBroader term (generic)BTG
Hierarchical generic relationship⇒ from generic term to specific termTerme spécifique (générique)TSG Narrower term (generic)NTG
Hierarchical partitive relationship⇒ from specific term to geneic termTerme générique (partitif)TGPBroader term (partitive)BTP
Hierarchical partitive relationship⇒ from generic term to specific termTerme spécifique (partitif)TSPNarrower term (partitive)NTP
Hierarchical instance relationship⇒ from specific term to generic termTerme générique (instance)TGIBroader term (instance)BTI
Hierarchical instance relationship⇒ from generic term to specific termTerme spécifique (instance)TSINarrower term (instance)NTI
Hierarchical relationshipHighest concept in the hierarchyTerme de têteTTTop TermTT
Associative relationship⇒ from decriptor to another descriptorTerme associé ; Voir aussiTA ; VARelated TermNT
Summary table of relationships in a thesaurus (fromA. Serres, Introduction à l’indexation, https://www.sites.univ-rennes2.fr/urfist/Supports/Indexation/Indexation4Langages.html)

The SKOS datamodel and its implementation in Opentheso

Thesauri can be described in SKOS (Simple Knowledge Organization System) format, whiwh is a W3C recommendation for representing document languages. This data model allows the publication, exchange and linking of structured vocabularies with Semantic Web technologies.

SKOS scheme (schem by Blandine Nouvel)

The classes of SKOS model and their equivalents in Opentheso:

SKOS classes DefinitionEquivalent in Opentheso
Labels 
skos:prefLabelDescriptor term.Preferred term
skos:altLabelNon descriptor term.Synonym
skos:hiddenLabelThe ‘hidden label’ allows to include wrong writtings of non-descriptor terms, integrated in the search but not visible to the user.Hidden synonym
Semantic relationships  
skos:broaderBroader concept.Broader concept
skos:narrowerNarrower concept.Narrower concept
skos:relatedRelated concept.Related concept
Annotations  
skos:noteNote.Note
skos:definitionDefinition.Definition
skos:scopeNoteScope, usage, use or explicative note: brief explanation on how to use a descriptor term.Scope note
skos:historyNoteHistory note: describe a changment in the form or the signification of a concept.History note
skos:exampleExample.Example
skos:editorialNoteNotes for the editorial managment of the thesaurus (comments).Editorial note
skos:changeNoteNotes for the editorial managment of the thesaurus (documenting a change).Change note
Alignment or equivalence with external standards 
skos:exactMatchExact equivalence.Exact match
skos:closeMatchClose equivalence.Close match
skos:broadMatchGeneric alignement links.Broad match
skos:narrowMatchSpecific alignment links.Narrow match
skos:relatedMatchAssociative alignment links.Related match
Concept et collection of concepts  
skos: conceptConcept.Concept
skos: collectionCollection of concepts.Group
Notations
skos:notationCode that identifies a concept.Notation

Plublishing your thesaurus

It is recommended that you write a presentation of your thesaurus on the home page. It is useful to specify the ‘metadata’ for the dissemination of a thesaurus – subject, context and date of creation, research project and term, institutions – and to indicate under which license it is published.

Citer cet article : « Best practices for structuring a thesaurus », par Alyssa Turgis. Publié sur Opentheso le 01/06/2022. Lien : https://opentheso.hypotheses.org/2776.

Bibliography

Aitchison, Jean, et Gilchrist, Alain, Construire un thésaurus. Manuel pratique, Paris, ADBS Éditions, 1992, 217 p.

Chichereau, Dominique, Contat ,Odile, Dégez, Danièle et al., « Les normes de conception, gestion et maintenance de thésaurus. Évolutions récentes et perspectives », Documentaliste-Sciences de l’Information, 2007/1 (Vol. 44), p. 66-74 [read online].

Dalbin, Sylvie, Yakovleff, Nathalie, Zysman, Hélène, ISO 25964-1- Thésaurus pour la recherche documentaire. Livre blanc, Saint-Denis, Afnor, 2013, 37 p.

Enssib, “Thésaurus”, 2013 [read online]

Glossaire des techniques de l’information, portail Joconde [read online].

Gouvernement du Québec, Politique d’édition du thésaurus de l’activité gouvernementale [read online].

Hudon, Michèle, « ISO 25964 : pour le développement, la gestion et l’interopérabilité des langages documentaires » Documentation et bibliothèques, vol. 58-3, 2012, p. 130–140 [read online].

Isaac, Antoine et Summers, Ed (ed.), SKOS : Simple Knowledge Organization System Primer. W3C Working Group Note 18 August 2009 [read online].

Keller, Loraine, Encadrer la réingénierie d’un thesaurus, mémoire pour obtenir le titre professionnel « Chef de projet en ingénierie documentaire », INTD, Conservatoire national des arts et métiers, Paris, 2013 [read online].

Serres, Alexandre, Introduction à l’indexation, URFIST Bretagne -Pays de Loire, 2003 [read online].

Alistair, Miles, Bechhofer, Sean, SKOS : Système simple d’organisation de connaissances. Référence. Recommandation W3C du 18 août 2009, trad. T. Francart [read online].

Zeng, Marcia Lei, Construction of Controlled Vocabularies, A Primer, 2005 [read online]


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