Chronological Subdivisions

Introduction

With the exception of some very general chronological subdivisions, which will be dealt with under Free-Floating Subdivisions, chronological or period subdivisions are normally different for each subject. As a result, subject authority records should exist for the vast majority of these headings.

The chronological subdivision is preceded by a |y subfield code.

You may search for these as described in the section on Topical Subdivisions.

Normally a chronological subdivision for the century is used in conjunction with a topical subject subdivision such as --History. Under place names, the number of allowed freefloating subdivisions is increased, including such options as --Civilization, --Economic conditions and --Social life and customs.

Authority records for these types of subject headings can be quite simple.

 DL FMT A RT z DT 04/04/98 R/DT none    STAT ln E/L n
 SRC   LANG ??? ROM ? MOD   UNIQUE n GOVT ? S/SYS a D/I ? SUBD ? NUM n S/TYP n
 NAME b SUBJ c SER b KIND a H/ESTAB a T/EVAL n IP a RULES n

 010:  : |a sh 85023999
 040:  : |a DLC |c DLC
 151: 0: |a China |x Civilization |y 1949-

Chronological subject subdivisions may also be set up based on the name of the historical period. The dates are also included as part of the heading.

 DL FMT A RT z DT 04/04/98 R/DT none    STAT ln E/L n
 SRC   LANG ??? ROM ? MOD   UNIQUE n GOVT ? S/SYS a D/I ? SUBD ? NUM n S/TYP n
 NAME b SUBJ c SER b KIND a H/ESTAB a T/EVAL b IP a RULES n

 010:  : |a sh 85024070
 040:  : |a DLC |c DLC
 053/1:  : |a DS751.92
 151: 0: |a China |x History |y Chin dynasty, 1115-1234
 400/1:30: |a Chin dynasty, |d 1115-1234

This type of subdivision is becoming rarer, as the Library of Congress is discontinuing their use, and changing some of the subdivisions already established, since these headings do not file in chronological order on the computer.

For this reason, if an original cataloguer feels that it is helpful, an additional "see reference" may be added to a chronological subdivision authority record, listing the dates before the phrase heading. However, this option should be employed sparingly, as it interferes with the process of updating the subject authority records.

Note, however, that the Library of Congress is gradually moving away from the practice of providing the name of the chronological period before the date.

 DL FMT A RT z DT 04/04/98 R/DT none    STAT ln E/L n
 SRC   LANG ??? ROM ? MOD   UNIQUE n GOVT ? S/SYS a D/I ? SUBD ? NUM n S/TYP n
 NAME b SUBJ c SER b KIND a H/ESTAB a T/EVAL b IP a RULES n

 010:  : |a sh 85024070
 040:  : |a DLC |c DLC
 053/1:  : |a DS751.92
 151: 0: |a China |x History |y Chin dynasty, 1115-1234
 400/1:30: |a Chin dynasty, |d 1115-1234
 451/2: 0: |a China |x History |y 1115-1234, Chin dynasty

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Searching Chronological Subdivisions

Note that it is always wise to use a shortened search string for chronological subdivisions, since many of these headings start out with open dates, which have later been closed. By using the shortened search string you will locate the bibliographic records which require updating to the more complete heading. In most instances there will not be a "search under" reference for the "old heading" since usually the old and new forms of the name index next to one another.

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Updating Chronological Subdivisions

There are two complications to the process of updating these headings. The first problem results from the fact that these open date headings are closed retroactively--sometimes years later. This can result in the situation where the date span no longer accurately represents the subject matter of the book. For example, in 1992, the subject heading Venezuela--History--1935- was closed, to Venezuela--History--1935-1974. At the time the book was catalogued, the open-ended date range was appropriate. However, the date range was closed a full 20 years after the fact. Therefore, it is possible that some of the books that were catalogued under the original heading, describe the period after 1974. Usually, the problem can be solved by adding another subject heading with a later time period--in this instance, Venezuela--History--1974-. However, if the book deals mostly with the period after 1974, then it would be more appropriate to use the new date span instead of the original one. When correcting such headings, if the book seems to cover a significantly different period of time, consult with the appropriate original cataloguer.

The second complication results from the fact that the Library of Congress has been known to establish both a closed date range for a shorter period of time and an open-ended date range--both of which headings begin with the same date. In this situation, if the appropriate subject heading is not immediately clear, consult with the appropriate subject area original cataloguer.

Besides these specific time periods, certain "generic" time periods are also authorized in the Free-Floating Subdivisions section. An example of this type of subdivision would be --History--19th century.

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