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Structure of the Indexing Language

Suitability for the LEMoN Armoury * Type of Indexing Language and
Pre-coordinate Headings vs. Post Co-ordinate Retrievial
Forms of Terms
Relationship Structures
Precision / Recall * Specificity * Exhaustivity * Weight of Aboutness vs. Meaning

*Relationship structures
Three types of semantic relationships are used to link terms in the LAT: equivalence, hierarchical, and associative.  Each is explained and demonstrated below.

(NOTE: These concepts are also discussed in ready-reference form in the LAT User Guide.)

Equivalence
ANSI/NISO Z39.19-2005 states that in any situation where a concept that can be expressed by more than one term, one term should be chosen as the preferred term [8.2].  All other terms that could be used to refer to the concept then become non-preferred terms.  Non-preferred terms in this situation retain an “equivalence relationship” to the preferred term, and cross-references are used to link the former to the latter.

The convention for expressing these relationships involves two shorthand terms: USE and UF.  USE directs a user from a non-preferred term to the preferred term, while UF indicates the alternative or “entry” terms gathered under a preferred term.

Example from the LAT:
bastard sword USE hand-and-a-half
hand-and-a-half UF bastard sword

In this case, “bastard sword” is popular slang for a type of sword more accurately termed “hand-and-a-half.”  Though “hand-and-a-half” refers in our thesaurus to a sword wielding style, this term can still be used as an adjective and therefore usurps the need to include “bastard sword” under the node label “<sword types>.”  Their relationship is synonymous because both terms refer to the same or nearly the same concept [8.2.1].

Hierarchical
In cases where preferred terms occupy differing levels of superordination and subordination, their relationship to one another can be expressed hierarchically [8.3].  This holds true for multiple types of hierarchies, including class/member and whole/part relationships.  The convention for expressing these relationships is to use BT (broader term) as a label for the superordinate term and NT (narrower term) to refer to the subordinate term.

Example from the LAT:
weapons
            NT edged weapons

edged weapons
            BT weapons
                        NT swords

Here, the shorthand expressions make it clear that “weapons” describes a class of items, while “edged weapons” exists as a member of the broader “weapons” class.  We can further define this relationship type as a generic hierarchical relationship, since some weapons are edged weapons, while all edged weapons are weapons [8.3.1].  (“Swords” is another, narrower category of member items falling under the class “edged weapons.”)  Not all hierarchical relationships in the LAT are generic; many are whole-part, showing which items form subsets or smaller parts of larger objects in the collection [8.3.3].

A special note should be made regarding our use of node labels.  These labels, which are indicated by their angle-bracketed notation in the thesaurus (e.g., <sword parts>), are not preferred terms.  Instead, they serve to show the conceptual division between sibling terms in a hierarchy [8.3.5].  By showing a semantic relationship between concepts, node labels function as “stand-in” broader terms within the thesaurus.  Under no circumstances can they be used as indexing terms.

Associative
Sometimes, relationships exist between terms that cannot be expressed through either equivalence or hierarchical means.  This usually occurs when terms are conceptually associated with one another in a way that is direct or strong enough to warrant explicit indication in the thesaurus [8.4].  The convention for expressing this relationship is the abbreviation RT (related term), which can describe associative relationships between terms in either the same hierarchy or different hierarchies.

Example from the LAT:
harmonically balanced
RT centre of percussion

            centre of percussion
                        RT harmonically balanced

In this example, “harmonically balanced” refers to a sword that has an optimized centre of percussion, usually located 25-30% of the way from the blade tip.  The term “centre of percussion” (the point on the blade that produces the least vibration on hard contact and delivers the most force to the target) refers to a concept that is essential to understanding a sword that is harmonically balanced.  These two terms neither refer to the same concept, as in an equivalence relationship, nor are they hierarchical neighbours.  Thus, we use the RT designation to display their connection to one another.