Section 4
Preferred Terms and Non-preferred Terms

Equivalent Terms

After collecting terms for your thesaurus, you need to decide which are equivalent terms. For purposes of indexing and searching, a set of equivalent terms will all be treated as though they meant the same thing and will be represented by a single preferred term.

Spelling and Synonyms

Sometimes, equivalent terms really do mean the same thing. So, it obviously makes sense to use a single preferred term to represent that one meaning.

A word may have more than one spelling; for example, "AESTHETICS" and "ESTHETICS".
Two different words may have essentially the same meaning; for example, "AUTOMATION" and "MECHANIZATION".

Quasi-synonyms

Sometimes, equivalent terms mean different things in ordinary language. For indexing and retrieval, it is better to group the different meanings together. Such equivalent terms are called quasi-synonyms.

Types of quasi-synonyms

Terms with overlapping meanings are sometimes treated as equivalent. For example, "GENIUSES" and "PRODIGIES" might be treated as equivalent, even though the two terms mean different things.

A term whose scope is included in that of another term is sometimes treated as equivalent. For example, "STEEL" might be treated as equivalent to "METAL" if it is not important to distinguish items on steel from items on other metals.

Sometimes opposites are treated as equivalent, because items on one are likely to be relevant to a query for the other. For example, "TRANSPARENCY" might be treated as equivalent to "OPACITY".

Preferred Terms

Preferred terms serve as focal points where all the information about a concept is collected.

Non-preferred Terms

Non-preferred terms are included in a thesaurus mainly to help users find the appropriate preferred terms. Non-preferred terms may also help to define the scope of preferred terms.

USE/UF

A non-preferred term is normally linked to a corresponding preferred term by a USE reference. The corresponding reference in the opposite direction if UF ("Used For").

For example,

PERIODICALS
USE SERIALS SERIALS
UF PERIODICALS
Here the preferred term is "SERIALS" and the corresponding non-preferred term is "PERIODICALS".

Choosing Preferred Terms

The following are some principles for choosing preferred terms, together with examples of applying them.

Guidelines	Examples
Usage	COOKING UF COOKERY ("Cooking" is the more commonly used word.)
Breadth	PLASTICS UF POLYETHYLENE ("Plastics" clearly means all plastics, of which polyethylene is only one.)
Disambiguation	AMERICAN LIBRARY ASSOCIATION UF ALA ("ALA" could stand for something else.)
Collocation	RAILWAY STATIONS UF TRAIN STATIONS (In an alphabetical sequence, "RAILWAY STATIONS" would appear near to "RAILWAYS" and other terms related to railways.)
Conciseness	MUCKRAKERS UF MUCKRAKING MOVEMENT (One word rather than two.)
Plural for countable objects	GEESE UF GOOSE (Geese are countable.)
Internal consistency	If you have decided to prefer the Latin names for plants, do so consistently.
External consistency	You might prefer "PIERS & WHARVES" to "LANDINGS", "BOAT LANDINGS", "DOCKS", "QUAYS", or "WHARVES" partly because that is what the Library of Congress Thesaurus for Graphic Material does.

Quiz on preferred terms (requires JavaScript)

Compound USE References

Instead of a single non-preferred term, one may sometimes instruct indexers and searchers to use more than one preferred term in combination. In such cases, the USE reference points to all the preferred terms, and the UF reference is often marked in some special way.

For example,

SNOWMOBILES
USE VEHICLES+SNOW
SNOW
UF+ SNOWMOBILES
VEHICLES
UF+ SNOWMOBILES

You are especially likely to do this if the non-preferred term consists of more than one word.

For example,

SCHOOL CAFETERIAS
USE CAFETERIAS+SCHOOLS
CAFETERIAS
UF+ SCHOOL CAFETERIAS
SCHOOLS
UF+ SCHOOL CAFETERIAS

On the other hand, you may choose not to make such a term a non-preferred term, even if it consists of more than one word.

Making Multi-word Terms Preferred

When should you allow a multi-word as a preferred term?

A term consisting of more than one word should typically be made a preferred term if

combining terms is not possible either at the indexing stage or at the searching stage
too many terms would otherwise be required to index an item
the resulting number of preferred terms is not too large
indexing and searching are generally easier using the compound term
the term is likely to be used frequently in indexing or searching
the term's components occur frequently in different syntactic relations; for example, "LIBRARY SCHOOLS", "SCHOOL LIBRARIES".
the term is needed in the structure of semantic relations; especially, if any narrower concepts are represented by preferred terms.
you are in doubt