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Thesaurus Structure

Relationships Between Terms

The NAL Agricultural Thesaurus includes hierarchical, equivalence and associative relationships among concepts.

Hierarchical Relationships

Hierarchical relationships are indicated by "Broader Term" and "Narrower Term" designations in the thesaurus. The hierarchical relationship is a distinguishing feature of the thesaurus in contrast to a simple list of alphabetically ordered terms. Superordinate "Broader Terms" represent more general concepts than subordinate "Narrower Terms":

Example
intercropping
Broader Terms
cropping systems
Narrower Terms
alley cropping

"alley cropping" is subordinate to "intercropping" since it is more specific type of intercropping, and "intercropping" belongs to a larger concept class of "cropping systems". This relationship suggests that if a searcher is interested in "cropping systems", they would also be interested in specific types of cropping systems such as "intercropping" and "alley cropping."

Equivalence Relationships

Equivalence relationships are made when two or more terms represent the same or nearly the same concept, e.g., synonymous terms, common names of organisms and their scientific equivalent, spelling variants, usage variants, and acronyms. For accurate, clear, and consistent indexing, only one term should be used to represent a concept.

The NALT contains:

  1. "Descriptors" or "preferred terminology," used to express concepts for indexing and retrieval. Descriptors are used by indexers to describe the subject content of materials;
  2. "Non-descriptors," which have the same or nearly the same meaning as their equivalent descriptors, but cannot be assigned to materials by indexers. Non-descriptors are also known as "non-preferred terms", or "lead-in terminology". They are included in the NAL Agricultural Thesaurus to direct users from "non-preferred" terms to the appropriate "descriptors" for indexing and retrieval.

Non-descriptors are identified by the "Use" and "Used for" designations, and appear in italics to alert users that these are non-preferred terms:

Example
Schizaphis graminum
Used for
greenbug
Toxoptera graminum

"Schizaphis graminum" is the descriptor. The terms "greenbug" and "Toxoptera graminum" serve as non-descriptors to direct thesaurus users to the appropriate descriptor for indexing and retrieval. This is how the corresponding equivalence relationships appear in the Thesaurus:

Example
greenbug
Use
Schizaphis graminum
Example
Toxoptera graminum
Use
Schizaphis graminum

"AND type" cross references are used occasionally, and are designated by "Use AND type" and "Used for AND type". This example instructs the indexer to assign the terms "alkalinity" and "water" for the concept of "alkaline water".

Example
alkaline water
Use AND type
alkalinity
Use AND type
water

These examples show how the reciprocal equivalence relationship: "Use for AND type", appears for the terms "alkalinity" and "water".

Example
alkalinity
Use for AND type
alkaline water
Example
water
Use for AND type
alkaline water

Associative Relationships

Associative relationships are designated by "Related Terms" reciprocal relationships. An associative relationship is made between terms that are conceptually related but are neither hierarchical or equivalence relationships in nature. Associative relationships serve to alert indexers and searchers that there are other related concepts in the Thesaurus that may be of interest to them. In these examples the process of "photosynthesis" is a related concept to "thylakoids", because thylakoids are the site of photosynthesis.

Example
photosynthesis
Related Terms
thylakoids
Example
thylakoids
Related Terms
photosynthesis

Notes

Scope Notes

Scope Notes serve to clarify the meaning and application of the term in relation to other terms in the thesaurus. In this example, the first part of the Scope Note gives guidance on the concept that the term represents and the second part gives guidance on which term to use for a related concept.

Example
anorexia
Scope Note
Use for the uncontrolled lack or loss of appetite for food; for the eating disorder characterized by the misperception of body image USE anorexia nervosa.

Source Notes

Source Notes serve to designate the authoritative work or organization from which the term was derived. Citations for sources are located in the Bibliography.

Example
at-risk population
Source
Joint Institute for Food Safety and Applied Nutrition

Definitions

Definitions appear as shown in the example below. The sources of definitions are acknowledged in the "Definition Source" field. Bibliographic citations for sources are given in the bibliography. Please consult our disclaimer regarding definitions.

Example
intercropping
Definition
Any pattern of planting a plant in or near other plants.
Definition Source
NAL Thesaurus Staff

Homographs

Homographs are terms in which the same spelling of a term represents two or more different concepts. Since it is necessary to adhere to the basic principle that each term in a thesaurus represent only one concept, the meanings of homographs are clarified by using a parenthetical qualifer that follows the term. This practice is in accordance with the NISO Z39.19 standard for Guidelines for the Construction, Format, and Management of Monolingual Thesauri:

Example
Togo (Africa)
Togo (Heteroptera)