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Glossary of terms relating to thesauri and other forms of structured vocabulary for information retrieval

Confusion often arises when different people use terms to mean different things. In drawing up the following list I am grateful for suggestions and comments from three consultant colleagues who specialise in the development and use of thesauri and other forms of structured vocabulary for information retrieval: Stella Dextre Clarke, Alan Gilchrist and Ron Davies. I have tried as far as possible to maintain consistency with definitions which we drafted for the revised British standards for thesaurus construction (BS 8723:2005 Structured vocabularies for information retrieval) and have taken some account of the definitions in the USA national standard, Z39.19. I do not claim that these definitions are "correct" and that other meanings are "wrong", but I hope that they will be found to be a consistent and well-defined set which will aid communication by encouraging everyone to use the same words with the same meaning. Discussions about some of the definitions are continuing, and they may change. Some of the definitions, notes and examples are my personal suggestions, and my colleagues may not agree with them. Comments and feedback on content or presentation are welcome and should be sent to me, Leonard Will

a posteriori relationship
use syntagmatic relationship
a priori relationship
use paradigmatic relationship
array
(a) a set of sibling terms or (b) a subset of sibling terms grouped under a node label which specifies a characteristic of division

e.g. in a this extract

vehicles
(vehicles by number of wheels)
- monocycles
- bicycles
- - motor bicycles
- - pedal bicycles
- tricycles
- four-wheeled vehicles
(vehicles by motive power)
- mechanically powered vehicles
- - motor bicycles
- - motor cars
- human powered vehicles
- - pedal bicycles
- hybrid human/mechanically powered vehicles
- - mopeds

the complete array of sibling terms under vehicles consists of

monocycles
bicycles
tricycles
four-wheeled vehicles
mechanically powered vehicles
human powered vehicles
hybrid human/mechanically powered vehicles

This may be subdivided into subsets by grouping under the node labels, forming two smaller arrays:

monocycles
bicycles
tricycles
four-wheeled vehicles

and

mechanically powered vehicles
human powered vehicles
hybrid human/mechanically powered vehicles
.

Another array, at a lower level, under the broader term bicycles, is composed of the two sibling terms

motor bicycles
pedal bicycles

See the note under characteristic of division on the options for dealing with hybrids such as mopeds.

authority file
use authority list
authority list
use for authority file
controlled vocabulary, generally of proper names, for use in naming particular entities consistently
Separate authority lists may be maintained for different types of entity; for example there may be separate lists for personal names, organization names and geographical names. The format of names used in an authority file should be documented and preferably accord with recognised standards. An example of a personal and corporate name authority file might look like this:

British Tabulating Machine Company
  merged into International Computers and Tabulators
Gates, Bill
  use for Gates, William Henry
Gates, William Henry
  use Gates, Bill
ICL
  use International Computers Limited
ICT
  use International Computers and Tabulators
International Computers and Tabulators
  created by merger of British Tabulating Machine Company and Powers-Samas
  subsequently International Computers Limited
International Computers Limited
  formerly International Computers and Tabulators
Powers-Samas
  merged into International Computers and Tabulators
Prime Computer Inc.
Science Museum (London). Library
Victory (ship)

browsing
finding information by examining lists or sequences of items, typically starting with general items and, on the basis of what has been found there, moving to more specific items
caption
statement of the subjects represented by a notation in a classification scheme
A caption may have to be read in conjunction with its hierarchical context. It need not be as complete or as self-contained as a scope note or even a preferred term in a thesaurus.
chain index
an index to a classification scheme, in which entries are generated by successive left truncation of strings of terms representing compound concepts

e.g. in the example of citation order, a compound concept is represented by the pre-coordinated string

bicycles - tyres - punctured - repairing - instruction books

In a classification scheme arranged in this way, everything on bicycles will be grouped together, but material on tyres or instruction books will be scattered. To provide index entries to allow these scattered topics to be found, we write the string in the reverse order, and successively truncate it from the left, making an index entry for each resulting substring:

instruction books - repairing - punctured tyres - bicycles
repairing - punctured tyres - bicycles
punctured tyres - bicycles
tyres - bicycles
bicycles

These entries are then arranged in alphabetical order:

bicycles
instruction books - repairing - punctured tyres - bicycles
punctured tyres - bicycles
repairing - punctured tyres - bicycles
tyres - bicycles

Each of these index entries would be followed by the appropriate notation to link it to its place in the classification scheme. As the citation order of this classification determines that everything about tyres for bicycles will be grouped together in the classified sequence, it is not necessary for the index to have entries such as tyres - bicycles - punctured, or other combinations and permutations of the terms in the string. A chain index is thus more economical than a fully permuted index, in which a string of five terms would generate 120 index entries.

The mechanical method of generating a chain index described here may be modified by editorial intervention to suppress entries which are likely to be unsought, and to combine terms grammatically to make the index entries more readable; this has been done in the above example where punctured tyres has been used rather than punctured - tyres.
characteristic of division
an attribute by which a concept can be subdivided into an array of narrower concepts each having a distinct value of that attribute

e.g. In the following, "number of wheels" and "motive power" are the characteristics by which the concept of "vehicles" is divided. These are shown in the node labels (vehicles by number of wheels) and (vehicles by motive power).

The concepts in an array should be mutually exclusive, having distinct values of the characteristic of division, though lower-level concepts can occur under more than one. For example, hybrids, such as mopeds (mechanically-assisted pedal cycles) are by definition both mechanically powered and human powered. They can therefore be listed as narrower terms of both concepts, as shown below. In some cases it may be desirable to provide explictly for such hybrids, as shown in the examples under array. The scope note should clarify whether a term such as human powered vehicles is to be used for vehicles that are exclusively or partially human-powered.

vehicles
(vehicles by number of wheels)
- vehicles without wheels
- monocycles
- bicycles
- - motor bicycles
- - pedal bicycles
- tricycles
- four-wheeled vehicles
- vehicles with more than 4 wheels
(vehicles by motive power)
- mechanically powered vehicles
- - mopeds
- - motor bicycles
- - motor cars
- human powered vehicles
- - mopeds
- - pedal bicycles

citation order
order in which preferred-terms or notations are combined in a pre-coordinate indexing system or a classification scheme to form strings representing compound concepts

The choice of citation order determines which concepts are the most important to be grouped together in a catalogue or list, and increases consistency in the construction of strings for similar subjects.

Citation order is usually specified in terms of the facets to which concepts belong or the roles that they play in relation to other concepts in the string. A sequence that is often appropriate, especially for technical subjects, is:

thing - kind - part - property - material - process - operation - system operated on - product - by-product - agent - space - time - form

e.g.
bicycles - tyres - punctured - repairing - instruction books
(thing) - (part) - (property) - (operation) - (form)

When concepts from two different arrays within a single facet are to be combined, the citation order is normally such that the array listed later in the schedule is cited first (takes priority in grouping). Thus if wines were grouped by into two arrays: first (wines by colour) and second (wines by country), the combined concepts would be listed under the second of these, thus:

wines
(wines by colour)
- red wines
- white wines
(wines by country)
- Australian wines
- - (Australian wines by colour)
- - red Australian wines
- - white Australian wines
- French wines
- - (French wines by colour)
- - red French wines
- - white French wines

It is possible to make additional entries under permutations of these citation orders of facets and arrays, but this not only increases the size of a catalogue but also leads to inconsistency as there is a risk that some permutations will be omitted. Some resources may be assigned one version of the complex concept and some another, so that there is not a complete list under either.

classification
grouping together of similar or related things and the separation of dissimilar or unrelated things and the arrangement of the resulting groups in a logical and helpful sequence
classification scheme
schedule of concepts, arranged by classification
A classification scheme may also include an index.
classified display
display of a thesaurus structure in which terms representing concepts are brought together because of the subjects to which they relate
Such a display may contain sections of hierarchical display, but may also bring together related terms from different facets, such as the people, activities and objects relating to a subject. Classified displays may include node labels containing facet names as well as node labels specifying characteristics of division. An example of a classified display is shown under node label.
coined term
a new term created to express a concept for which no suitable term exists in the required language.
collection
the set of documents that may be accessed by a structured vocabulary, whether the items in it are collected in one place or distributed over a network
complex concept
concept that combines two or more simpler concepts

human resource management combines the idea of people with their usefulness as resources requiring management

Complex concepts are sometimes expressed in a single word, but are more often conveyed by a multi-word term.

concept
unit of thought
The semantic content of a concept can be re-expressed by a combination of other and different concepts, which may vary from one language or culture to another. Concepts exist in the mind as abstract entities which are independent of the terms used to label them.
concept scheme
set of concepts, optionally including statements about semantic relationships between those concepts.
Thesauri, classification schemes, subject heading lists, taxonomies, terminologies, glossaries and other types of controlled vocabularies are all examples of concept schemes.
controlled vocabulary
prescribed list of terms or headings each one having an assigned meaning
Controlled vocabularies are designed for use in classifying or indexing documents and for searching them. They normally contain a unique preferred term for each concept or entity with links to that term from non-preferred terms. They may also show relationships between terms.
descriptor
use preferred term
document
use for information resource
item that can be classified or indexed in order that it may be retrieved
This definition refers not only to written and printed materials in paper or microform versions (for example, books, journals, diagrams, maps), but also to non-printed media, machine-readable and digitized records, Internet and intranet resources, films, sound recordings, people and organizations as knowledge resources, buildings, sites, monuments, three-dimensional objects or realia; and to collections of such items or parts of such items.
entry term
use non-preferred term
enumerative classification scheme
classification scheme in which all the concepts available for use are listed in the schedules
equivalence relationship
relationship between two terms that both represent the same concept
When two or more such terms are in the same monolingualthesaurus, one of them is designated a preferred term and the other(s) non-preferred term(s); the relationship is known as intra-vocabulary equivalence. When both terms are preferred terms in different thesauri, the relationship is known as cross-vocabulary equivalence.
facet
use for fundamental facet
grouping of concepts of the same inherent category

Examples of categories that may be used for grouping concepts into facets are: activities, disciplines, people, materials, living organisms, objects, places and times. e.g.
(1) animals, mice, daffodils and bacteria could all be members of a living organisms facet;
(2) digging, writing and cooking could all be members of an activities facet;
(3) Paris, the United Kingdom and the Alps could all be members of a places facet.

Categories are normally chosen so that facets are mutually exclusive; a concept cannot then occur in more than one facet. In a classification scheme, facets may be restricted to a single discipline, such as a diseases facet in medicine, or may be common facets such as people, time, place and form, which apply across all disciplines. Facets may be subdivided into mutually exclusive subfacets.

Some writers use the term "facet" to specify the role that a concept plays in a complex concept, as well as the category to which it belongs. For example, they may say that materials can belong to "raw materials" or "products" facets, and people may be in "agents" or "patients" facets. For clarity, it is better to avoid this usage, keeping the term "facet" for fundamental categories such as "materials" or "people" and specifying roles separately. Both facets and roles are used in setting up rules for citation order.

Other writers use the term "facet" to mean "attributes" or "properties", confusing them with characteristics of division. There may be multiple characteristics of division of concepts within a single facet, e.g. within a materials facet there may be a concept of wines, subdivided into several arrays, not mutually exclusive, each headed by a node label such as <wines by colour>, <wines by sweetness>, <wines by origin>, <wines by price> and so on. Any specific wine can be listed in several of these arrays. Searching by these is better called searching by parameters or characteristics rather than by facets.

facet analysis
analysis of subject areas into constituent concepts grouped into facets
facet indicator
notational device that indicates the start of a new facet within a synthesized compound classmark
Examples of facet indicators are the 0 in the Dewey Decimal Classification, and parentheses and quotation symbols in the Universal Decimal Classification. In the past the term facet indicator has been used as synonymous with node label but that usage should be avoided, to avoid confusion.
faceted classification scheme
classification scheme in which subjects are analysed into their constituent facets

Schedules are compiled for each facet, and terms or notations from these may be combined according to prescribed rules to express a complex concept.

folksonomy
a collection of terms allocated to resources by users in order to categorise or index them in a way that the users consider useful
Terms in folksonomies, often called tags, are typically added in an uncontrolled manner, without any underlying structure or principles. They may be idiosyncratic, but may also use current terminology more quickly than it can be incorporated into a controlled and structured scheme.
fundamental facet
use facet
glossary
a list of terms, together with definitions, specific to a given field of knowledge, usually presented in alphabetical order
Such terms are usually of a technical, abstruse or archaic nature. A glossary is often related to a specific document and appears as an appendix to it.
hierarchical display
display of a thesaurus structure based on broader/narrower concept relationships
In such a display narrower terms are commonly shown indented under the broader term which is their parent. Each hierarchy, starting from a "top term" contains terms from only a single facet or subfacet, so node labels containing facet names do not occur within hierachies, though they may be shown at the top of each. A hierarchical display may contain node labels specifying characteristics of division. An example of a hierarchical display is shown under characteristic of division.
homograph
one of two or more words that have the same spelling, but different meanings
e.g. The term bank could refer to a financial institution or the side of a river.
identifier
A specific term that is not included in a controlled vocabulary, but which may be assigned to a document because it is considered useful for retrieval
Identifiers are often proper names, trade names, codes, jargon and specialised terms. They should be distinguished from controlled vocabulary terms by being recorded in a separate field of a catalogue record or by being flagged in some way. Some computer systems assign a unique number or code to each concept or term for purposes of managing the vocabulary, and it may be known as a 'concept identifier', 'term identifier' or simply 'term ID'. This type of identifier should not be confused with the usage defined here.
indexing
intellectual analysis of the subject matter of a document to identify the concepts represented in it, and allocation of the corresponding preferred terms to allow the information to be retrieved
The term "subject indexing" is often used for this concept, but within a context that does not deal with other elements such as authors or dates, "indexing" is sufficient.
information resource
use document
information retrieval
all the techniques and processes used to provide for identifying items relevant to an information need, from a collection or network of documents
Selection and inclusion of items in the collection are included in this definition; likewise browsing and other forms of information seeking.
interoperability
ability of two or more systems or components to exchange information and to use the information that has been exchanged
Vocabularies can support interoperability by including relations to other semantic structures, by presenting data in standard formats and by using systems that support common computer protocols.
keyword
A word or phrase occurring in the natural language of a document that is considered significant for retrieval.
In addition to the above preferred meaning this word is also used loosely with the following two other possible meanings, which are often confused. The use of "keyword" with these meanings should be avoided.
  1. A preferred term from a controlled vocabulary, assigned to a document
  2. An identifier.
lead-in term
use non-preferred term
loan term
term borrowed from another language that has become accepted in the borrowing language
e.g. glasnost, gourmets
many-to-one mapping
mapping where two or more terms, notations or concepts in one vocabulary are represented by a single term, notation or concept in another vocabulary
mapping (process)
the process of establishing relationships between the terms, notations or concepts of one vocabulary and those of another
mapping (product of mapping process)
statements of the relationships between the terms, notations or concepts of one vocabulary and those of another
metadata
data that describes characteristics of a document
Metadata is essentially a catalogue record, providing (a) access points by which records of documents can be sorted or retrieved and (b) descriptive information, by which the relevance of a document can be assessed without consulting it in full. Preferred terms or notations selected during the indexing process are commonly applied as metadata elements to describe the subject of a document.
microthesaurus
subset of a thesaurus, usually containing terms from a subject area narrower than the scope of the whole thesaurus
The UNESCO thesaurus is subdivided into seven microthesauri; the UK Archival Thesaurus, based on the UNESCO thesaurus, is also subdivided into microthesauri, which it calls "fields of knowledge".
monohierarchical structure
hierarchical arrangement of concepts, in a thesaurus or classification scheme, in which each concept can have only one broader concept
Compare with polyhierarchical structure. In a monohierarchical structure, each concept can occur at only one place in the hierarchy and other broader term relationships have to be shown as related term relationships.

e.g. in a monohierarchical structure, the concept pianos cannot be listed as a narrower term of both keyboard instruments and stringed instruments; a choice has to be made of one of these concepts to determine its placing.

multilingual thesaurus
thesaurus using more than one language, in which each concept is represented by a preferred term in each of the languages, and there is a single structure of hierarchical and associative relationships between concepts which is independent of language.
multi-word term
term consisting of more than one word

e.g. human resource management.

Multi-word terms typically label complex concepts and are admissible in a thesaurus as preferred terms.

node label
label inserted into a hierarchical or classified display to show how the terms have been arranged

A node label contains one of two different types of information: either (1) the name of a facet or subfacet to which following terms belong (this type would be better called a "facet label", but unfortunately this usage is not established in the literature or standards); or (2) the attribute or characteristic of division by which an array of sibling terms has been sorted or grouped.

e.g. the following classified display starts with the facet "disciplines" and changes of facet are shown by node labels of type 1, shown in parentheses. A node label of type 2 is shown in angle brackets:

photography
- (people)
- photographic models
- - <photographic models by gender>
- - female photographic models
- - male photographic models
- photographers
- (operations)
- taking photographs
- developing
- printing
- (objects)
- cameras
- photographs
- - black and white photographs
- - colour photographs

non-descriptor
use non-preferred term
non-preferred term
use for entry term; lead-in term; non-descriptor
term that is not assigned to documents but is provided as an entry point in a thesaurus or alphabetical index
A non-preferred term is followed by a reference to the appropriate preferred term or terms, e.g. hounds USE dogs
notation
symbol or group of symbols representing a simple or compound concept

Notation may be used to sort and/or locate concepts in a pre-determined systematic order, and optionally to display how concepts have been structured and grouped. A notation can provide the link between alphabetical and systematic lists in a thesaurus and between the alphabetical index and the classified sequence of a classification scheme.

e.g., partial schedule showing notation in the left-hand column:

P200    photography
P250    - - photographic equipment
P251    - - - camera accessories
P251.3  - - - - flash guns
P251.5  - - - - tripods
P253    - - - cameras and camera components
P253.1  - - - - camera components
P253.13 - - - - - camera lenses
P253.15 - - - - - camera viewfinders
P253.2  - - - - cameras

notation system
set of symbols, with rules for combining them to create notations for concepts

This set may be any selection of numerals, upper and lower case alphabetic characters, and punctuation symbols. The larger the set of symbols on which the notation is based, the greater the number of concepts that can be represented by distinct notations of the same length.

Punctuation marks may be used in notations:

  1. to show relationships between concepts, e.g. 53:61 "physics in relation to medicine";
  2. to act as facet indicators, showing that the subsequent symbols refer to a concept from a different facet, e.g. 61(94) "medicine in Australia";
  3. to show where the notation may be abbreviated if desired, e.g. ; 641.5'68, "cooking for special occasions", may be abbreviated to 641.5, "cooking";
  4. to break up long strings to make them easier to read, e.g the period and spaces in 635.977 138 9 "fertilisers for flowering trees" or KVQ EOM MUR "unemployment in rural communities in India".
one-to-many mapping
mapping where a single term, notation or concept in one vocabulary is represented by two or more terms, notations or concepts in another vocabulary
one-to-one mapping
mapping where a single term, notation or concept in one vocabulary is represented by a single term, notations or concepts in another vocabulary
The representations in the two vocabularies may or may not be identical.
ontology
specification of the concepts of a domain and their relationships, structured to allow computer processing and reasoning
As the nature of the relationships can be specified as part of the ontology, many more types of relationship are possible than in a thesaurus.
orphan term
a preferred term that has no hierarchical relationships
paradigmatic relationship
use for a priori relationship; semantic relationship
relationship between concepts which is inherent in the concepts themselves

Such relationships are shown in a structured vocabulary, independently of any indexed document.

parametric searching
searching for concepts with specific values of characteristics of division

e.g. searching for wines for which the colour is red and the alcohol content is from 5% to 10%.

This type of search is for concepts that occur within one or more arrays of a single facet, e.g. narrower terms of wine in a "materials" facet grouped under the node labels (wine by colour) and (wine by alcohol content). In some systems it is possible to search for a range of values rather than just for specific values.

It is to be distinguished from searches for compound concepts which may be made up of concepts from different facets, such as wine from a "materials" facet combined with red colour and alcohol content from a "properties" facet.

polyhierachical structure
hierarchical arrangement of concepts, in a thesaurus or classification scheme, in which each concept can have more than one broader concept

Compare with monohierarchical structure. In a polyhierarchical structure, a single concept can occur at more than one place in the hierarchy. Its attributes and relationships, and specifically its scope note and its narrower and related terms, are the same wherever it occurs.

e.g. in a polyhierarchical structure, pianos may be listed as a narrower term of both keyboard instruments and stringed instruments.

post-coordinate indexing
system of indexing in which the subject of a document is analysed into its constituent concepts by an indexer but the preferred terms so allocated are not combined until they are selected by a user at the search stage

e.g. when using post-coordinate indexing, a manual on bicycle repair might be assigned the three separate preferred terms

  • bicycles
  • repairing
  • instruction books

Someone searching for such a manual would compose a search statement such as (bicycles AND repairing AND instruction books). The document would also be retrieved by a search for (bicycles AND instruction books) or for any one or more of the preferred terms. Compare pre-coordinate indexing.

precision
measure of retrieval performance defined by R/T, where R is the number of relevant items retrieved and T is the total number of items retrieved
pre-coordinate indexing
system of indexing in which the preferred terms allocated to a particular document are syntactically combined in one or more sequences representing the only combinations available for retrieval purposes

e.g. when using pre-coordinate indexing, a manual on bicycle repair might be assigned the indexing string made up of three preferred terms in combination:

bicycles - repairing - instruction books

This brings all aspects of repairing bicycles together in a catalogue or browsing list, and might be followed by

bicycles - repairing - tools

There would be no direct alphabetical access to this subject under repairing, instruction books, or tools. This does not mean that the individual concepts within a pre-coordinated string cannot be searched for separately, either as controlled preferred terms or as free text, but such methods are not part of the pre-coordinate indexing system. Compare post-coordinate indexing.

preferred term
use for descriptor
term specified by a controlled vocabulary for use to represent a concept when indexing.

e.g. schools; school uniform; costs of schooling; teaching.

A preferred term should preferably be a noun or noun phrase.

quasi-synonym
one of two or more terms whose meanings are generally regarded as different in ordinary usage but which may be treated as labels for the same concept, for the purposes of a given controlled vocabulary
e.g. diseases, disorders; earthquakes, earth tremors
recall
measure of retrieval performance defined by R/N, where R is the number of relevant items retrieved and N is the total number of relevant items in the collection
schedule
terms, notations, cross-references and scope notes set out to exhibit the content and structure of a structured vocabulary
scope note
note which defines or clarifies the meaning of a concept as it is used in the structured vocabulary
A preferred term used to label a concept may have several meanings in normal usage. A scope note may restrict the concept to only one of these meanings, and may refer to other concepts that are included or excluded from the scope of the concept being defined.
search thesaurus
vocabulary intended to assist searching even though it has not been used to index the documents being searched

Search thesauri are designed to facilitate choice of terms and/or expansion of search expressions to include terms for broader, narrower or related concepts, as well as synonyms. Optionally, a normal thesaurus may be used as a search thesaurus.

semantic network
actual or virtual graphical representation of concepts and the relationships between them

A semantic network is a way of representing an ontology. The vertices of the network represent concepts and the edges represent semantic relationships between them. The vertices are sometimes called "nodes", which are not to be confused with the node labels of a thesaurus or a faceted classification.

semantic relationship
use paradigmatic relationship
sibling term
one of two or more terms with the same immediate broader term
e.g. In the following, biology, chemistry, geology and physics are sibling terms. So are nuclear physics and quantum physics.

sciences
- biology
- chemistry
- - analytical chemistry
- geology
- physics
- - nuclear physics
- - quantum physics

source vocabulary
language or vocabulary which serves as a starting point when seeking a corresponding term in another language or vocabulary
When working with two vocabularies, the source vocabulary for one concept may be the target vocabulary for another concept.
specificity
capability of a structured vocabulary to express a subject in depth and in detail
Specificity has an important influence on retrieval performance, as it determines the accuracy with which concepts may be pinpointed, and consequently the facility to exclude unwanted documents.
string
sequence of preferred terms representing a compound concept in a pre-coordinate indexing system
structured vocabulary
set of terms, headings or concept codes and their inter-relationships which may be used to support information retrieval
A structured vocabulary may also be used for other purposes. In the context of information retrieval, the vocabulary should be accompanied by rules for how to apply the terms.
subfacet
a subdivision of a facet, based on inherent categories

Subfacets, like facets, should be defined so that they are mutually exclusive. For example, an "agents" facet might be subdivided into "individuals" and "organisations" subfacets; an "activities" facet might be subdivided into transitive "actions" and intransitive "processes" subfacets.

Some writers use the term "subfacet" as synonymous with array, or with the slightly broader meaning of the whole subtree of concepts grouped under a node label showing a characteristic of division, rather than just the first level array of sibling terms. I suggest that it should not be used with these meanings, as the intuitive meaning is "a subdivision of a facet" and we already have the terms "array" and "subtree" for the other meanings.

subject heading list
use subject heading scheme
subject heading scheme
use for subject heading list
controlled vocabulary comprising single terms available for subject indexing, plus rules for combining the single terms in strings
The principles for constructing subject heading lists differ from the principles of thesaurus construction. Subject heading lists may have provision for the construction of pre-coordinated indexing strings including headings and one or more levels of subheading.
synonym
one of two or more terms whose meanings are considered to be the same in a wide range of contexts
Abbreviations and their full forms may be treated as synonyms. e.g. HIV, human immunodeficiency virus; guarantees, warranties
synonym ring
group of terms that are considered equivalent for the purposes of retrieval.
Synonym rings are particularly useful in search thesauri, used for searching unindexed material, where a search for any one of the terms in the ring can retrieve occurrences of any of the terms in the ring.
syntactic relationship
use syntagmatic relationship
syntagmatic relationship
use for a posteriori relationship; syntactic relationship
relationship between concepts that exists only because they occur together in a document being indexed
Such relationships are not generally valid in contexts other than the document being indexed, and therefore they do not form part of the structure of a thesaurus.
synthetic classification scheme
classification scheme in which users can synthesize terms or notation for complex concepts from lists of simpler concepts
target vocabulary
language or vocabulary in which a term is sought corresponding to an existing term in a source language or vocabulary
When working with two vocabularies, the target vocabulary for one concept may be the source vocabulary for another concept.
taxonomy
monohierarchical classification of concepts, as used, for example, in the classification of biological organisms
The above definition is a personal opinion; the definition proposed in BS8723-3 is "structured vocabulary using classificatory principles as well as thesaural features, designed as a navigation tool for use with electronic media". The term is used loosely to mean various types of classification schemes, subject heading lists or thesauri, particularly when applied to the indexing of Internet resources. In my opinion this use should be avoided because of its vagueness and uncertainty; when a non-specific meaning is intended, concept scheme or controlled vocabulary should be used instead.
term
word or phrase used to label a concept
Terms in a thesaurus can be either preferred terms or non-preferred terms.
thesaurus
controlled vocabulary in which concepts are represented by preferred terms, formally organized so that paradigmatic relationships between the concepts are made explicit, and the preferred terms are accompanied by lead-in entries for synonyms or quasi-synonyms
The purpose of a thesaurus is to guide both the indexer and the searcher to select the same preferred term or combination of preferred terms to represent a given subject.
topic map
concept scheme conforming to the specification given in the international standard ISO/IEC 13250 : Topic maps

ISO/IEC 13250 gives the following three definitions for "topic map":
a) A set of information resources regarded by a topic map application as a bounded object set whose hub document is a topic map document conforming to the SGML architecture defined by this International Standard.
b) Any topic map document conforming to the SGML architecture defined by this International Standard, or the document element (topicmap) of such a document.
c) The document element type (topicmap) of the topic map document architecture.

The introduction to ISO/IEC 13250 says: "In general, the structural information conveyed by topic maps includes:
- groupings of addressable information objects around topics ('occurrences'), and
- relationships between topics ('associations')".

vocabulary control
restriction of choice of indexing terms to those in a specified list
This restriction increases the likelihood of indexers and searchers choosing the same term to label a concept.
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