School of Information Management & Systems. Fall 2000.
142 Access to American Cultural Heritages.   Buckland.

1. People don't always agree what a document is about. A matter of point of view.
2. Relying on the words in the document (title, text, etc.) has limitations. Very common words are usually ignored as a hindrance: THE, OF, FROM..,... "Stop words".
3. You need language for description - and language is culturally based. Use of "natural language" (ordinary use of words) results in inconsistency since there are unlimited different ways to describe something. "Unnatural language" can provide consistency, by
(a) "Controlled", limited, standardized, and stylized use of words (List of subject headings, thesaurus, controlled vocabulary); or
(b) Artificial notation to denote and arrange subjects, e.g. a library or other classification using numerals.
  Groups have their cultures and so vary in specialized terminology, concepts, views, and values, so description needs to be situational, for some group, for some purpose.
3. Combinations of topics, e.g. "The physics of music." The cataloger/indexer isolates the different aspects ("facets") of the subject. How do you find a particular combination?
(a) The indexer can assign a descriptor for each separate aspect of the subject matter. The searcher examines the list of books associated with each facet, then compares the lists to see which books occurs on all of these lists, i.e. has that combination of descriptors. Check the list of books on "Physics" and the list of books on "Music" and identify the books on both lists. ("Post-coordinate" searching). This "Boolean searching" is typical of online bibliographic databases.
(b) Alternatively, the cataloger can define and label each combination before anyone searches ("Pre-coordinate indexing"): (i) General books on "Cherokee Indians" in one list; (ii) General books on "Poetry" in another list; but (iii) Books on " Cherokee Indian Poetry" (a combination) only in a separate third list. And "Poetry about Cherokee Indians." in a fourth. For manual searches in card catalogs and printed indexes conventions are needed to govern arrangement: File under C for "Cherokee Indian Poetry" or under P for "Poetry -- Cherokee Indian"? This has carried over into "eXact SUbject" searches in online library catalogs.   N.B. Pre- and post-coordinate systems should be logically equivalent.
(c) More powerful "second generation" online library catalogs, e.g. MELVYL, use a curious combination. The indexing data available is precoordinate subject cataloging from the Library of Congress Subject Headings list. So these headings can be searched as composed with F XSU   They are also decomposed into individual words indexed individually so that the words can be searched separately or in any combination as specified by the searcher, i.e. post-coordinate searching, using FIND SW (=Subject keyWord) followed by one or more words. Thus a post-coordinate ("subject keyword") searching capability in provided (F SW) as well as exact pre-coordinate searching (F XSU).
4. Other clues, e.g. title words, language, date, and authorship are often useful, e.g. Find records for a few books on a subject using a search on title words, then using Display LONG or D SU to reveal the subject headings.
5. Library catalogs use the Library of Congress Subject Headings, in big red volumes usually kept near online terminals, which makes elaborate use of subheadings to denote subtopics, form (e.g. "dictionaries"), place, time, etc. There are also cross-references, e.g.
USE [= use some other heading] and its reciprocal USE FOR - for synonyms.
Dowsing USE Divining-rod; Divining Rod UF Dowsing. Usually relates synonyms.
NT = "See also the Narrower Term" and its reciprocal
BT = "See also the Broader Term": Dogs NT Spaniels; Spaniels BT Dogs.
RT = "See also the related term": Birds RT Ornithology.
SA = "See also": Dog breeds SA names of specific breeds, e.g. bloodhound, collies,...
Ability testing SA subdivision Ability testing under subjects, e.g. Dentists--Ability testing.