Introduction to DDC


About the Introduction

1.1 This Introduction explains the basic principles and structure of the Dewey Decimal
Classification (DDC) system.

1.2 The Introduction is intended to be used in conjunction with the Glossary and the Manual.
The Glossary defines terms used in the Introduction and elsewhere in the Classification.
The Manual offers advice on classifying in difficult areas, and explains how to choose
between related numbers.

Classification: What It Is and What It Does

2.1 Classification provides a system for organizing knowledge. Classification may be used
to organize knowledge represented in any form, e.g., books, documents, electronic

2.2 Notation is the system of symbols used to represent the classes in a classification system.
In the Dewey Decimal Classification, the notation is expressed in Arabic numerals. The
notation gives both the unique meaning of the class and its relation to other classes. The
notation provides a universal language to identify the class and related classes, regardless
of the fact that different words or languages may be used to describe the class.

History, Current Use, and Development of the Dewey Decimal Classification

3.1 The Dewey Decimal Classification is a general knowledge organization tool that is
continuously revised to keep pace with knowledge. The system was conceived by Melvil
Dewey in 1873 and first published in 1876. The DDC is published in print and
electronic versions by OCLC Online Computer Library Center, Inc. OCLC owns all
copyright rights in the Dewey Decimal Classification, and licenses the system for a
variety of uses.

3.2 The DDC is the most widely used classification system in the world. Libraries in more
than 135 countries use the DDC to organize and provide access to their collections, and
DDC numbers are featured in the national bibliographies of more than sixty countries.
Libraries of every type apply Dewey numbers on a daily basis and share these numbers
through a variety of means (including WorldCat, the OCLC Online Union Catalog).
Dewey is also used for other purposes, e.g., as a browsing mechanism for resources on
the web.

3.3 The DDC has been translated into over thirty languages. Translations of recent full and
abridged editions of the DDC are completed or underway in Arabic, Chinese, French,
German, Greek, Hebrew, Icelandic, Italian, Korean, Norwegian, Russian, Spanish, and


3.4 One of Dewey's great strengths is that the system is developed and maintained in a
national bibliographic agency, the Library of Congress. The Dewey editorial office is
located in the Decimal Classification Division of the Library of Congress, where
annually the classification specialists assign over 110,000 DDC numbers to records for
works cataloged by the Library. Having the editorial office within the Decimal
Classification Division enables the editors to detect trends in the literature that must be
incorporated into the Classification. The editors prepare proposed schedule revisions
and expansions, and forward the proposals to the Decimal Classification Editorial Policy
Committee (EPC) for review and recommended action.

3.5 EPC is a ten-member international board whose main function is to advise the editors
and OCLC on matters relating to changes, innovations, and the general development of
the Classification. EPC represents the interests of DDC users; its members come from
public, special, and academic libraries, and from library schools.

Overview of the Dewey Decimal Classification

Conceptual Framework

4.1 The DDC is built on sound principles that make it ideal as a general knowledge
organization tool: meaningful notation in universally recognized Arabic numerals, well-
defined categories, well-developed hierarchies, and a rich network of relationships
among topics. In the DDC, basic classes are organized by disciplines or fields of study.
At the broadest level, the DDC is divided into ten main classes, which together cover the
entire world of knowledge. Each main class is further divided into ten divisions, and
each division into ten sections (not all the numbers for the divisions and sections have
been used).

4.2 The main structure of the DDC is presented in the DDC Summaries in the beginning of
volume 2. The first summary contains the ten main classes. The second summary
contains the hundred divisions. The third summary contains the thousand sections. The
first and second summaries are provided for browsing purposes, and the headings do not
necessarily match the name of the sections found in the schedules.


4.3 The ten main classes are:

000 Computers, information & general reference
100 Philosophy & psychology
200 Religion
300 Social sciences
400 Language
500 Science
600 Technology
700 Arts & recreation
800 Literature
900 History & geography

4.4 Class 000 is the most general class, and is used for works not limited to any one specific
discipline, e.g., encyclopedias, newspapers, general periodicals. This class is also used
for certain specialized disciplines that deal with knowledge and information, e.g.,
computer science, library and information science, journalism. Each of the other main
classes (100 - 900) comprises a major discipline or group of related disciplines.

4.5 Class 100 covers philosophy, paranormal phenomena, and psychology.

4.6 Class 200 is devoted to religion. Both philosophy and religion deal with the ultimate
nature of existence and relationships, but religion treats these topics within the context of
revelation, deity, and worship.

4.7 Class 300 covers the social sciences. Class 300 includes sociology, anthropology,
statistics, political science, economics, law, public administration, social problems and
services, education, commerce, communications, transportation, and customs.

4.8 Class 400 comprises language, linguistics, and specific languages. Literature, which is
arranged by language, is found in 800.

4.9 Class 500 is devoted to the natural sciences and mathematics. The natural sciences (500)
describe and attempt to explain the world in which we live.

4.10 Class 600 is technology. Technology consists of utilizing the sciences to harness the
natural world and its resources for the benefits of humankind.

4.11 Class 700 covers the arts: art in general, fine and decorative arts, music, and the
performing arts. Recreation, including sports and games, is also classed in 700.

4.12 Class 800 covers literature, and includes rhetoric, prose, poetry, drama, etc. Folk
literature is classed with customs in 300.


4.13 Class 900 is devoted to history and geography. When a work is a story of events that
have transpired or an account of existing conditions in a particular place or region, it is
classed in 900. A history of a specific subject is classed with the subject.

4.14 Since the parts of the DDC are arranged by discipline, not subject, a subject may appear
in more than one class. For example, "clothing" has aspects that fall under several
disciplines. The psychological influence of clothing belongs in 155.95 as part of the
discipline of psychology; customs associated with clothing belong in 391 as part of the
discipline of customs; and clothing in the sense of fashion design belongs in 746.92 as
part of the discipline of the arts.


4.15 Arabic numerals are used to represent each class in the DDC. The first digit in each
three-digit number represents the main class. For example, 500 represents science. The
second digit in each three-digit number indicates the division. For example, 500 is used
for general works on the sciences, 510 for mathematics, 520 for astronomy, 530 for
physics. The third digit in each three-digit number indicates the section. Thus, 530 is
used for general works on physics, 531 for classical mechanics, 532 for fluid mechanics,
533 for gas mechanics. The DDC uses the convention that no number should have fewer
than three digits; zeros are used to fill out numbers.

4.16 A decimal point, or dot, follows the third digit in a class number, after which division by
ten continues to the specific degree of classification needed. The dot is not a decimal
point in the mathematical sense, but a psychological pause to break the monotony of
numerical digits and to ease the transcription and copying of the class number. A
number should never end in a 0 anywhere to the right of the decimal point.

Principle of Hierarchy

4.17 Hierarchy in the DDC is expressed through structure and notation.

4.18 Structural hierarchy means that all topics (aside from the ten main classes) are part of all
the broader topics above them. The corollary is also true: whatever is true of the whole is
true of the parts. This important concept is called hierarchical force. Certain notes
regarding the nature of a class hold true for all the subordinate classes, including
logically subordinate topics classed at coordinate numbers. (For a discussion of notes
with hierarchical force, see paragraphs 7.10 - 7.17 and 7.20 - 7.22.)

Because of the principle of hierarchical force, hierarchical notes are usually given
only once—at the highest level of application. For example, the scope note at

700 applies to 730, to 736, and to 736.4. The words "Description, critical appraisal . . ."
found in the scope note at 700 also govern the critical appraisal of carving in 736
Carving and carvings, and of wood carving in 736.4 Wood. In order to understand the
structural hierarchy, the classifier must read up and down the schedules (and remember
to turn the page).

4.19 Notational hierarchy is expressed by length of notation. Numbers at any given level are
usually subordinate to a class whose notation is one digit shorter; coordinate with a class
whose notation has the same number of significant digits; and superordinate to a class
with numbers one or more digits longer. The underlined digits in the following example
demonstrate this notational hierarchy:

600 Technology (Applied sciences)
630 Agriculture and related technologies
636 Animal husbandry
636.7 Dogs
636.8 Cats

"Dogs" and "Cats" are more specific than (i.e., are subordinate to) "Animal husbandry";
they are equally specific as (i.e., are coordinate with) each other; and "Animal
husbandry" is less specific than (i.e., is superordinate to) "Dogs" and "Cats."

4.20 Sometimes, other devices must be used to express the hierarchy when it is not possible or
desirable to do so through the notation. Special headings, notes, and entries indicate
relationships among topics that violate notational hierarchy. A dual heading is used
when a subordinate topic is the major part of the subject; the subject as a whole and the
subordinate topic as a whole share the same number (e.g., 599.9 Hominidae Homo
sapiens). A see reference leads the classifier to subdivisions of a subject located outside
the notational hierarchy. A centered entry (so called because its numbers, heading, and
notes appear in the center of the page) constitutes a major departure from notational
hierarchy. A centered entry is used to indicate and relate structurally a span of numbers
that together form a single concept for which there is no specific hierarchical notation
available. In the DDC, centered entries are always flagged typographically by the
symbol > in the number column.

Classifying with the DDC

5.1 Classifying a work with the DDC requires determination of the subject, the disciplinary
focus, and, if applicable, the approach or form. (For a discussion of approach or form,
see paragraph 8.3.)

Determining the Subject of a Work

5.2 Classifying a work properly depends first upon determining the subject of the work in

hand. A key element in determining the subject is the author’s intent.

(A) The title is often a clue to the subject, but should never be the sole source of
analysis. For example, Who Moved My Cheese? is a work on coping with
change, not a work related to the culinary arts. Likewise, a title with specific
terms that are subdivisions of a field may in fact use such terms symbolically to
represent the broader topic. For example, titles containing terms like
chromosomes, DNA, double helix, genes, and genomes may use these terms
symbolically to represent the whole subject of biochemical genetics.

(B) The table of contents may list the main topics discussed. Chapter headings
may substitute for the absence of a table of contents. Chapter subheadings
often prove useful.

(C) The preface or introduction usually states the author's purpose. If a foreword
is provided, it often indicates the subject of the work and suggests the place of
the work in the development of thought on the subject. The book jacket or
accompanying material may include a summary of the subject content.

(D) A scan of the text itself may provide further guidance or confirm preliminary
subject analysis.

(E) Bibliographical references and index entries are sources of subject information.

(F) Cataloging copy from centralized cataloging services is often helpful by
providing subject headings, classification numbers, and notes. Such copy
appears in online services, and on the verso of the title page of many U.S.,
Australian, British, and Canadian books as part of Cataloging-in-Publication
(CIP) data. Data from these sources should be verified with the book in hand,
since the cataloging record is based on prepublication information.
(G) Occasionally, consultation of outside sources such as reviews, reference works,
and subject experts may be required to determine the subject of the work.

Determining the Discipline of a Work

5.3 After determining the subject, the classifier must then select the proper discipline, or
field of study, of the work.

5.4 The guiding principle of the DDC is that a work is classed in the discipline for which it

is intended, rather than the discipline from which the work derives. This enables works
that are used together to be found together. For example, a general work by a zoologist
on agricultural pest control should be classed in agriculture, not zoology, along with
other works on agricultural pest control.

5.5 Once the subject has been determined, and information on the discipline has been found,
the classifier will turn to the schedules. The summaries are a good means of mental
navigation. The headings and notes in the schedules themselves and the Manual provide
much guidance. The Relative Index may help by suggesting the disciplines in which a
subject is normally treated. (For a discussion of the summaries, see paragraph 7.1; for a
discussion of the Manual, see paragraphs 10.1 - 10.6; for a discussion of the Relative
Index, see paragraphs 11.1 - 11.15.)

5.6 If the Relative Index is used, the classifier must still rely on the structure of the
Classification and various aids throughout to arrive at the proper place to classify a work.
Even the most promising Relative Index citations must be verified in the schedules; the
schedules are the only place where all the information about coverage and use of the
numbers may be found.

More Than One Subject in the Same Discipline

5.7 A work may include multiple subjects treated separately or in relation to one another
from the viewpoint of a single discipline. Use the following guidelines in determining
the best placement for the work:

(A) Class a work dealing with interrelated subjects with the subject that is being acted
upon. This is called the rule of application, and takes precedence over any other
rule. For instance, class an analytical work dealing with Shakespeare's influence
on Keats with Keats. Similarly, class a work on the influence of the Great
Depression on 20th century American art with American art.

(B) Class a work on two subjects with the subject receiving fuller treatment.

(C) If two subjects receive equal treatment, and are not used to introduce or
explain one another, class the work with the subject whose number comes first
in the DDC schedules. This is called the first-of-two rule. For example, a
history dealing equally with the United States and Japan, in which the United
States is discussed first and is given first in the title, is classed with the history

of Japan because 952 Japan precedes 973 United States.

Sometimes, specific instructions are given to use numbers that do not come first
in the schedules. For example, at 598, the note "class comprehensive works on
warm-blooded vertebrates in 599" tells the classifier to ignore the first-of-two rule
and class a work on birds (598) and mammals (599) in 599, which is the
comprehensive number for warm-blooded vertebrates.

Also disregard the first-of-two rule when the two topics are the two major
subdivisions of a subject. For example, collection systems (628.142) and
distribution systems (628.144) taken together constitute 628.14 Collection and
distribution systems. Works covering both of these topics are classed in 628.14
(not 628.142).

(For a discussion of the first-of-two rule versus preference order, see paragraph
9.6; for a discussion of comprehensive numbers, see paragraphs 7.17 and 7.20 -

(D) Class a work on three or more subjects that are all subdivisions of a broader
subject in the first higher number that includes them all (unless one subject is
treated more fully than the others). This is called the rule of three. For example,
a history of Portugal (946.9), Sweden (948.5), and Greece (949.5) is classed with
the history of Europe (940).

(E) Subdivisions beginning with zero should be avoided if there is a choice
between 0 and 1–9 at the same point in the hierarchy of the notation.
Similarly, subdivisions beginning with 00 should be avoided when there is a
choice between 00 and 0. This is called the rule of zero. For example, a
biography of an American Methodist missionary in China belongs in 266
Missions. The content of the work can be expressed in three different

266.0092 biography of a missionary
266.02373051 foreign missions of the United States in China
266.76092 biography of a United Methodist Church missionary

The last number is used since it has no zero at the fourth position.

More Than One Discipline

5.8 Treating a subject from the point of view of more than one discipline is different from
treating several subjects in one discipline. Use the following guidelines in determining
the best placement for the work:

(A) Use the interdisciplinary number provided in the schedules or Relative Index if
one is given. An important consideration in using such an interdisciplinary
number is that the work must contain significant material on the discipline in
which the interdisciplinary number is found. For example, 305.231 (a sociology
number) is provided for interdisciplinary works on child development. However,
if a work that is interdisciplinary with respect to child development gives little
emphasis to social development and a great deal of emphasis to the psychological
and physical development of the child (155.4 and 612.65, respectively), class it in
155.4 (the first number in the schedules of the next two obvious choices). In
short, interdisciplinary numbers are not absolute; they are to be used only when
applicable. (For a discussion of interdisciplinary numbers, see paragraphs 7.17,
7.20 - 7.21, and 11.8 - 11.9.)

(B) Class works not given an interdisciplinary number in the discipline given the
fullest treatment in the work. For example, a work dealing with both the
scientific and the engineering principles of electrodynamics is classed in 537.6 if
the engineering aspects are introduced primarily for illustrative purposes, but in
621.31 if the basic scientific theories are only preliminary to the author's
exposition of engineering principles and practices.

(C) When classifying interdisciplinary works, do not overlook the possibilities of
main class 000 Computers, information & general reference, e.g., 080 for a
collection of interviews of famous people from various disciplines.

Any other situation is treated in the same fashion as those found in the instructions at
More Than One Subject in the Same Discipline (paragraph 5.7).


Table of Last Resort

5.9 When several numbers have been found for the work in hand, and each seems as good as
the next, the following table of last resort (in order of preference) may be used as a
guideline in the absence of any other rule:

Table of last resort

(1) Kinds of things
(2) Parts of things
(3) Materials from which things, kinds, or parts are made
(4) Properties of things, kinds, parts, or materials
(5) Processes within things, kinds, parts, or materials
(6) Operations upon things, kinds, parts, or materials
(7) Instrumentalities for performing such operations

For example, surveillance by border patrols could be classed in either 363.285 Border
patrols, or 363.232 Patrol and surveillance. Choose 363.285 since border patrols are a
kind of police service, while patrol and surveillance are processes performed by police

5.10 Do not apply this table or any other guideline if it appears to disregard the author's
intention and emphasis.

How DDC 22 Is Arranged

6.1 DDC 22 is composed of the following major parts in four volumes:

Volume 1
(A) New Features in Edition 22: A brief explanation of the special features and
changes in DDC 22

(B) Introduction: A description of the DDC and how to use it

(C) Glossary: Short definitions of terms used in the DDC

(D) Index to the Introduction and Glossary


(E) Manual: A guide to the use of the DDC that is made up primarily of extended
discussions of problem areas in the application of the DDC. Information in the
Manual is arranged by the numbers in the tables and schedules. Directly
following the Manual is an appendix explaining the policies of the Library of
Congress Decimal Classification Division.

(F) Tables: Six numbered tables of notation that can be added to class numbers to
provide greater specificity

(G) Lists that compare Editions 21 and 22: Relocations and Discontinuations; Reused

Volume 2
(H) DDC Summaries: the top three levels of the DDC

(I) Schedules: The organization of knowledge from 000 - 599

Volume 3
(J) Schedules: The organization of knowledge from 600 - 999

Volume 4
(K) Relative Index: An alphabetical list of subjects with the disciplines in which they
are treated subarranged alphabetically under each entry

Key Features of the Schedules and Tables


7.1 Summaries provide an overview of the structure of classes. Three types of summaries
appear in the DDC:

(A) DDC Summaries, the summaries of the top three levels of the DDC, are found at
the front of the schedules in volume 2. (For a discussion of DDC Summaries, see
paragraphs 4.2 – 4.13.)

(B) Two-level summaries are provided for each main class and division of the

schedules and main numbers of Table 2 with subdivisions that extend beyond
forty pages. See the summaries at the beginning of
Table 2 —4 Europe Western Europe and 370 Education for examples of
two-level summaries.

(C) Single-level summaries in the schedules and tables provide an overview of classes
with subdivisions that cover between four and forty pages. For example,
382 International commerce (Foreign trade) has the following summary:


382.01 - .09 Standard subdivisions
.1 General topics of international commerce
.3 Commercial policy
.4 Specific products and services
.5 Import trade
.6 Export trade
.7 Tariff policy
.9 Trade agreements


7.2 Entries in the schedules and tables are composed of a DDC number in the number
column (the column at the left margin), a heading describing the class that the number
represents, and often one or more notes. DDC numbers are listed in groups of three
digits for ease of reading and copying. All entries (numbers, headings, and notes) should
be read in the context of the hierarchy. (For a discussion of the principle of hierarchy,
see paragraphs 4.17 - 4.20.)

7.3 The first three digits of schedule numbers (main classes, divisions, sections) appear only
once in the number column, when first used. They are repeated at the top of each page
where their subdivisions continue. Subordinate numbers appear in the number column,
beginning with a decimal point, with the initial three digits understood.

7.4 Table numbers are given in full in the number column of the tables, and are never used
alone. There are six numbered tables in DDC 22:

T1 Standard Subdivisions

T2 Geographic Areas, Historical Periods, Persons
T3 Subdivisions for the Arts, for Individual Literatures, for Specific
Literary Forms
T3A Subdivisions for Works by or about Individual Authors
T3B Subdivisions for Works by or about More than One Author
T3C Notation to Be Added Where Instructed in Table 3B, 700.4,
791.4, 808 - 809
T4 Subdivisions of Individual Languages and Language Families
T5 Ethnic and National Groups
T6 Languages

Except for notation from Table 1 (which may be added to any number unless there is an
instruction in the schedules or tables to the contrary), table notation may be added only
as instructed in the schedules and tables. (For a detailed discussion of the use of the six
tables, see paragraphs 8.3 - 8.18.)

7.5 When a subordinate topic is a major part of a number, it is sometimes given as a part of a
dual heading. For example:

—72 Middle America Mexico

599.9 Hominidae Homo sapiens

7.6 Some numbers in the schedules and tables are enclosed in parentheses or square
brackets. Numbers and notes in parentheses provide options to standard practice.
Numbers in square brackets represent topics that have been relocated or discontinued, or
are unassigned. Square brackets are also used for standard subdivision concepts that are
represented in another location. Bracketed numbers should never be used. (For a
discussion of options, see paragraphs 12.1 - 12.7; for a discussion of relocations and
discontinuations, see paragraphs 7.24 - 7.25; for a discussion of bracketed standard
subdivisions, see paragraph 7.26.)

7.7 Standard subdivisions are also bracketed under a hook number, that is, a number that
has no meaning in itself, but is used to introduce specific examples of a topic.
Hook numbers have headings that begin with "Miscellaneous," "Other," or "Specific";
and do not contain add notes, including notes, or class-here notes. For example:

652.302 Specific levels of skill


[.302 01–.302 09] Standard subdivisions

Do not use; class in 652.3001–652.3009


7.8 Notes are important because they supply information that is not obvious in the notational
hierarchy or in the heading with regard to order, structure, subordination, and other
matters. Notes may appear in the record for a number or a span of numbers. Notes may
also appear at the beginning of a table. Footnotes are used for instructions that apply to
multiple subdivisions of a class, or to a topic within a class. Individual entries in the
Manual are also considered notes.

7.9 Notes in the schedules and tables generally appear in the following order: revision,
former-heading, definition, number-built, standard-subdivisions-are added, variant-
name, scope, including, class-here, arrange, add (including subdivisions-are-added),
build, preference, discontinued, relocation, class-elsewhere, see-reference, see-also
reference, see-Manual, and option notes.

7.10.1 The notes below (A) describe what is found in the class and its subdivisions; (B)
identify topics in standing room, i.e., topics with insufficient literature to have their own
number; (C) describe what is found in other classes; and (D) explain changes in the
schedules and tables. Other notes are described in the sections on number building
(paragraphs 8.1 - 8.22), citation and preference order (paragraphs 9.1 - 9.6), the Manual
(paragraphs 10.1 - 10.6), and options (paragraphs 12.1 - 12.5).

Notes in categories (A) and (C) have hierarchical force (i.e., are applicable to all the
subdivisions of a particular number). Those in category (B) do not have hierarchical

(A) Notes That Describe What Is Found in a Class

7.11 Definition notes indicate the meaning of a term in the heading. For example:

364 Criminology
Crime and its alleviation


7.12 Scope notes indicate whether the meaning of the number is narrower or broader than
is apparent from the heading. For example:

700 The arts Fine and decorative arts

Description, critical appraisal, techniques, procedures, apparatus,
equipment, materials of the fine, decorative, literary, performing,
recreational arts

7.13 Number-built notes identify and explain the source of built numbers included in the
schedules and tables. Built numbers are occasionally included in the schedules or
tables to provide additional information or to indicate exceptions to regular add
instructions. For example:

353.132 63 Foreign service

Number built according to instructions under 352 - 354

Class here consular and diplomatic services

7.14 Former-heading notes are given only when the heading associated with a class number
in the previous edition has been altered to such a degree that the new heading bears little
or no resemblance to the previous heading, even though the meaning of the number has
remained substantially the same.

659.131 5 Industrial advertising

Former heading: Advertising directed to vocational uses

7.15 Variant-name notes are used for synonyms or near synonyms. For example:

332.32 Savings and loan associations

Variant names: building and loan associations, building societies,
home loan associations, mortgage institutions


7.16 Class-here notes list major topics in a class. These topics may be broader or narrower
than the heading, overlap it, or define another way of looking at essentially the same
material. Topics in class-here notes are considered to approximate the whole of the
class. For example:

371.192 Parent-school relations

Class here parent participation in schools; comprehensive works
on teacher-parent relations

Standard subdivisions may be added for any topic in a class-here note. (For a
detailed discussion of the use of standard subdivisions for concepts that approximate
the whole of a class, see paragraphs 8.3 - 8.10 and the beginning of Table 1.)

7.17 Class-here notes are also used to indicate where interdisciplinary and comprehensive
works are classed. Interdisciplinary works treat a subject from the perspective of more
than one discipline. For example:

391 Costume and personal appearance

Class here interdisciplinary works on costume, clothing, fashion

Comprehensive works treat a subject from various points of view within a single
discipline. Comprehensive works may be stated or implied in a class-here note. For

641.815 Breads and bread-like foods

Class here comprehensive works on baked goods (stated)

—411 5 Highland

Class here Scottish Highlands (implied)

(B) Including Notes (Notes That Identify Topics in Standing Room)

7.18 Including notes identify topics that have "standing room" in the number where the note
is found. Standing room numbers provide a location for topics with relatively few works
written about them, but whose literature may grow in the future, at which time they may
be assigned their own number. For example:

362.16 Extended care medical facilities

Including convalescent homes, sanatoriums for persons suffering from
chronic diseases

Standard subdivisions cannot be added for topics in standing room, nor are other
number-building techniques allowed.

7.19 Entries in the taxonomic schedules in 579–590 may have two including notes.
The first including note contains the scientific taxonomic names at or above the level of
family. The second one contains common and genus names. For example:

593.55 Hydrozoa

Including Chondrophora, Hydroida, Milleporina, Pteromedusae,
Siphonophora, Stylasterina, Trachylina

Including hydras, Portuguese man-of-war


(C) Notes That Describe What Is Found in Other Classes

7.20 Class-elsewhere notes lead the classifier to interrelated topics, or distinguish among
numbers in the same notational hierarchy. They are used to show preference order, to
lead to the comprehensive or interdisciplinary number, to override the first-of-two rule,
or to lead to broader or narrower topics in the same hierarchical array that might
otherwise be overlooked. They may point to a specific number, or to a concept scattered
throughout the schedules. All notes that begin with the word "class" are class-elsewhere
notes, except when they begin with "class here."

791.43 Motion pictures

Class photographic aspects of motion pictures in 778.53; class
made-for-TV movies, videotapes of motion pictures in 791.45

370.15 Educational psychology

Class interdisciplinary works on psychology in 150. Class
psychology of a specific topic in education with the topic,
plus notation 019 from Table 1, e.g., psychology of special
education 371.9019

155.4 Child psychology

Class interdisciplinary works on child development in 305.231


7.21 See references lead from a stated or implied comprehensive number for a concept to the
component (subordinate) parts of that concept in a different notational hierarchy. See
references also lead from the interdisciplinary number for a concept to treatment of the
concept in other disciplines. A see reference may point to a specific number, or to a
concept scattered throughout the schedules. Each see reference begins with the word
"For" and appears in italics. For example:

577.7 Marine ecology

Class here saltwater ecology

For salt lake ecology, see 577.639; for saltwater wetland
and seashore ecology, see 577.69

305.4 Women

Class here interdisciplinary works on women, on females

For a specific aspect of women not provided for here, see the
aspect, e.g., women's suffrage 324.623, legal status of women

Throughout Table 2, see references (often in footnote form) lead from the implied
comprehensive number for a jurisdiction, region, or feature to its subordinate parts in
other classes.

—411 5 Highland

Class here *Scottish Highlands

*For a specific part of this jurisdiction, region, or feature, see the part and
follow instructions under —4 - 9


7.22 See-also references lead the classifier to related topics. They are reminders that minor
differences in wording and context can imply differences in classification. Each see-also
reference appears in italics. For example:

584.3 Liliidae

Class here Liliales, lilies

For Orchidales, see 584.4

See also 583.29 for water lilies

(D) Notes That Explain Changes or Irregularities in the Schedules and Tables

7.23 Revision notes warn users that there have been changes in the subdivisions of a class
since the previous edition. A complete or extensive revision is always introduced by a
revision note that appears first under the heading of the class affected. (There are no
complete or extensive revision notes in DDC 22.)

7.24 Discontinued notes indicate that all or part of the contents of a number have been moved
to a more general number in the same hierarchy, or have been dropped entirely. For

[306.853] Suburban family

Number discontinued; class in 306.85

616.852 23 Panic disorder

Use of this number for comprehensive works on anxiety disorders
discontinued; class in 616.8522

7.25 Relocation notes state that all or part of the contents of a number have been moved to a
different number. For example:

[624.5] Suspension and cable-stayed bridges

Relocated to 624.23

381.149 Discount stores

Discount stores that are retail stores relocated to 381.15

The former number is usually given at the new number, either in the heading or in the
appropriate note. For example:

624.23 Suspension and cable-stayed bridges [both formerly 624.5]

381.15 Outlet stores

Class here discount stores that are outlet stores [formerly
381.149] . . .

7.26 Do-not-use notes instruct the classifier not to use all or part of the regular standard
subdivision notation or an add table provision in favor of a special provision, or
standard subdivisions at a broader number. When the whole standard subdivision
should not be used, the note appears under a bracketed standard subdivision; when
only part of the standard subdivision is displaced, the part displaced is specified. For

[374.809] Historical, geographic, persons treatment

Do not use; class in 374.9

320.409 Historical and persons treatment

Do not use for geographic treatment; class in 320.41 - 320.49

Number Building

8.1 The classifier will often find that to arrive at a precise number for a work it is necessary
to build or synthesize a number that is not specifically listed in the schedules. Such built
numbers allow for greater depth of content analysis. They are used only when
instructions in the schedules make them possible (except for standard subdivisions,
which are discussed in paragraphs 8.3 - 8.10). Number building begins with a base

number (always stated in the instruction note) to which another number is added.

8.2 There are four sources of notation from which to build numbers: (A) Table 1 Standard
Subdivisions; (B) Tables 2 - 6; (C) other parts of the schedules; and (D) add tables in the

(A) Adding Standard Subdivisions from Table 1

8.3 A standard subdivision represents a recurring physical form (such as a dictionary,
periodical, or index) or approach (such as history or research) and thus is applicable to
any subject or discipline that covers or approximates the whole of the meaning of the
number. Here are a few examples with the standard subdivision concept underlined (in
some cases an extra 0 precedes the standard subdivision according to instructions found
in the schedules):

150.5 Periodical on psychology
230.003 Dictionary of Christianity
340.02573 Directory of lawyers in the U.S.
401 Philosophy of language
507.8 Use of apparatus and equipment in the study and teaching of
science, e.g., science fair projects
624.0285 Computer applications in civil engineering
796.912092 Biography of a figure skater
808.0071 Teaching of rhetoric

Further instructions on using Table 1 are found at the beginning of Table 1. See also
Manual notes on selected standard subdivisions.

8.4 Standard subdivisions are not usually listed in the schedules except where needed to fill
out three-digit numbers, e.g., 605 Serial publications, and in a few other instances.
Standard subdivisions may be listed in the schedules when the subdivisions have special
meanings, when extended notation is required for the topic in question, or when notes are
required. The rest of standard subdivisions from Table 1 may be used with their regular

8.5 Notation from Table 1 Standard Subdivisions may be added to any number in the
schedules unless there is a specific instruction to the contrary. The classifier should never
use more than one zero in applying a standard subdivision unless instructed to do so. If

more than one zero is needed, the number of zeros is always indicated in the schedules.
When using standard subdivisions with numbers built by adding from Tables 2 - 6 or
other parts of the schedules, be sure to check the table or schedule used for the segment
preceding the standard subdivision for special instructions on the number of zeros.

8.6 Do not add multiple standard subdivisions to the same number except when specifically
instructed to do so, and in a few other instances. A second standard subdivision may be
added with standard subdivisions that have changed or extended meanings. For
example, notation 03 from Table 1, the standard subdivision for encyclopedias, may be
added to 370.15 Educational psychology to represent encyclopedias of educational
psychology 370.1503 because the regular meaning of 370.15 (scientific principles) has
been discontinued to 370.1 and replaced by an extended meaning of the standard
subdivision for psychological principles at this number. When standard subdivisions are
displaced to nonzero numbers (usually for geographic treatment), the full range of
standard subdivisions may be added, e.g., the management of penal institutions in Great
Britain 365.941068.

8.7 Standard subdivisions should not be used where redundant, i.e., where the subdivision
means the same as the base number, or where application of the standard subdivision
would needlessly segregate material by aspects not emphasized by the author. For
example, do not add notation 024694, which represents the subject for carpenters, to
topics in 694 Carpentry, since works on a subject are written primarily for its
practitioners. Likewise, do not add notation 0905, which represents the state-of-the-art,
to general works on a subject because most users will expect to find such works in the
main number. Special care should be taken in adding standard subdivisions to built
numbers, since the standard subdivision applies to the whole number and not just part of
the number.

8.8 The table of preference at the beginning of Table 1 yields to two other rules, the rule of
application and the rule of zero. By the rule of application, teaching financial
management in hospital administration is classed in 362.110681, not 362.11071, even
though notation 07 is above notation 068 in the table of preference. The rule of zero
overrides the table of preference when standard subdivisions are displaced to nonzero
positions, e.g., management of prisons in Great Britain 365.941068, not 365.068 as
would be the case if prisons in Great Britain were classed in 365.0941. (For a discussion
of the rule of application and rule of zero, see paragraph 5.7; for a discussion of
displaced standard subdivisions, see paragraphs 7.26 and 8.6.)

8.9 The most important caveat with respect to standard subdivisions is that they are added
only for works that cover or approximate the whole of the subject of the number. For
example, a work on black widow spiders of California should be classed in the number
for spiders 595.44 (not 595.4409794, the number for spiders in California). The
classifier should not attempt to specify California because black widow spiders do not
approximate the whole universe of spiders in California, and there is not a specific
number available for black widows. Likewise, class a work on the De Havilland 98
Mosquito (a specific British World War II fighter-bomber) in the number for fighter-
bombers 623.7463 (not 623.7463094109044, the number for British fighter-bombers in
World War II).

8.10 Standard-subdivisions-are-added notes indicate which topics in a multiterm heading
may have standard subdivisions added for them because the designated topics are
considered to approximate the whole of the subject. For example:

639.2 Commercial fishing, whaling, sealing

Standard subdivisions are added for commercial fishing,
whaling, sealing together; for commercial fishing alone

Standard-subdivisions-are-added notes do not have hierarchical force.

(B) Adding from Tables 2–6

8.11 The classifier may be instructed to add notation from Tables 2 - 6 to a base number from
the schedules or to a number from a table. A summary of the use of each table follows.
Further instructions on using Tables 2 - 6 are found at the beginning of each table. See
also the Manual notes for Tables 2 - 6.

8.12 Table 2 Geographic Areas, Historical Periods, Persons. The major use of Table 2 is
with notation 09 from Table 1, where it can be added to every number in the schedule
unless there are specific instructions to the contrary. For example, reading instruction in
the primary schools of Australia is 372.40994 (372.4 reading instruction in primary
schools + 09 Historical, geographic, persons treatment from Table 1 + 94 Australia from
Table 2). Notation from Table 2 is also added through the use of other standard
subdivisions from Table 1 (e.g., standard subdivisions 025, 074).

8.13 Area notation is sometimes added directly to schedule numbers, but only when specified

in a note. For example:

373.3–373.9 Secondary education in specific continents, countries, localities

Add to base number 373 notation 3 - 9 from Table 2, e.g.,
secondary schools of Australia 373.94

8.14 Table 3 Subdivisions for the Arts, for Individual Literatures, for Specific Literary
Forms. These subdivisions are used in class 800 as instructed, usually following numbers
for specific languages in 810 - 890. Table 3C subdivisions are also added as instructed
to numbers in Table 3B, 700.4, 791.4, and 808 - 809.

8.15 Table 4 Subdivisions of Individual Languages and Language Families. These
subdivisions are used as instructed in class 400, following numbers for designated
specific languages or language families in 420 - 490.

8.16 Table 5 Ethnic and National Groups. Notation from Table 5 is added through the use of
standard subdivision 089 from Table 1, e.g., Ceramic arts of Chinese artists throughout
the world is 738.089951 (738 Ceramic arts + 089 Ethnic and national groups from
Table 1 + 951 Chinese from Table 5).

8.17 Table 5 notation may also be added directly to schedule numbers, but only when
specified in a note. For example:

155.84 Specific ethnic and national groups

Add to base number 155.84 notation 05 - 99 from Table 5, e.g.,
ethnopsychology of African Americans 155.8496073

8.18 Table 6 Languages. The major uses of Table 6 notation are to provide the
basis for building a specific language number in 490 (to which notation from Table 4
is sometimes added) and to provide the basis for building a specific literature number
in 890 (to which notation from Table 3 is sometimes added). Table 6 notation is
also used in Table 2 under —175 Regions where specific languages predominate, and
at various points in the schedules.

(C) Adding from Other Parts of the Schedules


8.19 There are many instructions to make a direct addition to a number from another part of
the schedules. For example:

809.935 Literature emphasizing subjects

Add to base number 809.935 notation 001 - 999, e.g., religious works
as literature 809.9352, biography and autobiography as literature

In this example, the 2 in 809.9352 comes from 200 Religion, the 92 in 809.93592 from
920 Biography, genealogy, insignia.

8.20 In many cases, part of a number may be added to another number upon instruction. For

372.011 Elementary education for specific objectives

Add to base number 372.011 the numbers following 370.11 in
370.111 - 370.119, e.g., character education 372.0114

In this example, 4 comes from 370.114 Moral, ethical, character education. Sometimes
numbers are taken from more than one place in the schedules; in such cases the
procedure for the second addition is the same as for the first.

(D) Adding from Tables Found in the Schedules

8.21 Add tables in the schedules provide numbers to be added to designated schedule
numbers (identified by a symbol and accompanying footnoted instruction); these tables
must be used only as instructed.
For example:

616.973 *Contact allergies

Class here allergic contact dermatitis, allergies of skin

The asterisk in the entry above leads to the following footnote: "Add as instructed
under 616.1 - 616.9." The add table at 616.1 - 616.9 is used only for diseases tagged

with an asterisk or for diseases in class-here notes under headings tagged with an
asterisk. Notation from the add table, such as 061 Drug therapy, may be used for
616.973 Contact dermatitis (tagged with an asterisk) and for allergic contact dermatitis
and allergies of skin (in the class-here note).

8.22 Subdivisions-are-added notes indicate which terms in a multiterm heading may have
subdivisions applied to them. For example:

616.51 *Dermatitis, photosensitivity disorders, urticaria

Subdivisions are added for dermatitis, photosensitivity disorders,
urticaria together; for dermatitis alone

Citation and Preference Order

9.1 Citation and preference order must be considered when multiple aspects or
characteristics of a subject (such as age, area, gender, historical periods, national origin)
are provided for in the Classification, and a single work treats more than one of them.

Citation Order

9.2 Citation order allows the classifier to build or synthesize a number using two or more
characteristics (facets) as specified in instruction notes. Success in building a DDC
number requires determining which characteristics apply to a specific work, and then
determining from the instructions in the schedule the sequence in which the facets will
be ordered.

9.3 Citation order is always carefully detailed in number-building instructions. For example:

909.04 History with respect to ethnic and national groups

Add to base number 909.04 notation 05 - 99 from Table 5, e.g.,
world history of Jews 909.04924; then add 0 and to the result add
the numbers following 909 in 909.1 - 909.8, e.g., world history of
Jews in 18th century 909.0492407

For a work on the world history of the Jews in the 18th century, this note stipulates

the following citation order for the individual facets of the full subject: world history
+ specific ethnic or national group + historical period. The historical period is
introduced by the facet indicator 0.

Preference Order

9.4 If there is no provision to show more than one of the aspects or characteristics, it is a
matter of preference (because a choice must be made among several characteristics).
Preference notes supply either an instruction or table establishing the order in which to
make the choice. An example of a preference instruction is found at 305.9:

305.9 Occupational and miscellaneous groups

Unless otherwise instructed, class a subject with aspects
in two or more subdivisions of 305.9 in the number coming last,
e.g., unemployed librarians 305.9092 (not 305.90694)

In this case, the base subject is a group of persons; the two characteristics are
employment status and occupational status. The occupation of librarian (305.9092) falls
after unemployed status (305.90694) in the DDC hierarchy; following the instructions in
the preference note, the characteristic that must be chosen is librarian (305.9092). (For
an example of a preference instruction using a class-elsewhere note, see paragraph 7.20.)

9.5 An example of a table indicating preference order is found at 305:

305 Social groups

Unless other instructions are given, observe the following table of
preference, e.g., African American male youths
305.235108996073 (not 305.3889607300835 or 305.896073008351):

Persons with disabilities and illnesses, gifted persons 305.908
Age groups 305.2
Groups by sex 305.3 - .4
Social classes 305.5
Religious groups 305.6
Ethnic and national groups 305.8

Language groups 305.7
Occupational and miscellaneous groups 305.9
(except 305.908)

9.6 Classifiers often must distinguish between preference order instructions and the first-
of-two rule in the same schedule. If the work treats two subjects, apply the first-of-
two rule. If the work treats two aspects of the same subject, apply the preference
order instructions. When the preference order instruction is to class with the last, the
first-of-two rule and the preference order instructions may lead the classifier in opposite
directions. For example, a bibliography of newspapers and pamphlets giving equal
treatment to each would be classed according to the first-of-two rule in 011.33
(bibliography of pamphlets) rather than 011.35 (bibliographies of newspapers). A
bibliography of microform newspapers (i.e., newspapers in microform form) would be
classed according to the preference note at 011.1 - 011.8: "Unless other instructions are
given, class a subject with aspects in two or more subdivisions of 011.1 - 011.8 in the
number coming last . . ."; thus, the bibliography of microform newspapers would be
classed in 011.36 (bibliographies of microforms) rather than 011.35 (bibliographies of
newspapers). (For a discussion of the first-of-two rule, see paragraph 5.7.)

The Manual

10.1 The Manual gives advice on classifying in difficult areas, and provides guidance on
choosing between related numbers.

10.2 See-Manual references in the schedules and tables refer the classifier to the Manual
for additional information about a certain number, range of numbers, or choice
among numbers. In some cases, the see-Manual reference refers only to a portion of
a longer Manual note, or topic narrower than the numbers in the heading, e.g., "See
Manual at 930-990: Historic preservation." The see-Manual reference is repeated in
the entries for each of the numbers or number spans covered in the Manual note. For
example, "See Manual at 004.21 vs. 004.22, 621.392" is listed in the entries for 004.21,
004.22, and 621.392.

10.3 Brief Manual-like notes are sometimes given directly in the schedule or table entry.
For example:

631.583 Controlled-environment agriculture


Most works on use of artificial light in agriculture will be classed
in 635.0483 and 635.9826

Arrangement and Format of the Manual

10.4 The Manual is arranged by table and schedule numbers, with the broadest span coming
before entries for narrower spans or individual numbers. Manual notes are entered under
the preferred or "if-in-doubt" number. If there is no if-in-doubt number, prefer the
interdisciplinary number.

10.5 The Manual note heading summarizes the contents of the note. The terms in the Manual
note headings need not match the terms associated with the same number(s) in
the tables and schedules if the note is narrower than the number, or the note refers to
more than one number.


510, T1—0151 vs. 003, T1—011


10.6 If the Manual note is very long, or part of the note focuses on a topic narrower than the
heading, subheadings may be provided. For example:

T1—068 vs. 353-354

Public administration and management in specific fields

Exceptions (subheading)

The Relative Index

11.1 The Relative Index is so named because it relates subjects to disciplines. In the
schedules, subjects are distributed among disciplines; in the Relative Index, subjects
are arranged alphabetically, with terms identifying the disciplines in which they are
treated subarranged alphabetically under them. For example:

Hospitals 362.11
accounting 657.832 2
animal husbandry 636.083 2
architecture 725.51
armed forces 355.72
Civil War (United States) 973.776
construction 690.551
energy economics 333.7964
institutional housekeeping 647.965 1
landscape architecture 712.7
law 344.032 11
liability law 346.031
meal service 642.56
pastoral theology 206.1
Christianity 259.411
social theology 206.762 11
Christianity 261.832 11
social welfare 362.11
United States Revolutionary War 973.376
World War I 940.476
World War II 940.547 6
see also Health services

In some cases the term implies rather than states the discipline. In the example above,
the discipline of architecture is listed, but the discipline of military science is implied
by "armed forces."

11.2 The Relative Index is primarily an index to the DDC as a system. It includes most
terms found in the schedules and tables, and terms with literary warrant for concepts
represented by the schedules and tables. The Relative Index is not exhaustive. If the
term sought is not found, the classifier should try a broader term, or consult the

schedules and tables directly. The schedules and tables should always be consulted
before a number found in the Relative Index is applied.

Arrangement and Format of the Relative Index

11.3 Index entries are arranged alphabetically word by word, e.g., Birth order precedes
11.4 Birthday. Entries with the same word or phrase but with different marks of
punctuation are arranged in the following order:

Term. Subheading
Term (Parenthetical qualifier)
Term, inverted term qualifier
Term as part of phrase

Initialisms and acronyms are entered without punctuation and are filed as if spelled as
one word. Hyphens are ignored and treated as a space. Terms indented below the
main headings are alphabetized in one group even though they may be a mixture of
disciplines, topical subheadings, and, to a limited extent, words that form phrases or
inverted phrases when combined with the main heading.

11.4 Class numbers are listed in groups of three digits for ease of reading and copying.
The spaces are not part of the numbers and do not represent convenient places to
abridge the number.

11.5 See-also references are used for synonyms and for references to broader terms (but
only when three or more new numbers will be found at the synonym or broader term),
and for references to related terms (which may provide only one or two new numbers).

11.6 See-Manual references lead the classifier to relevant discussions in the Manual.

11.7 Numbers drawn from Tables 1 - 6 are prefixed by T1 through T6.
(For a complete listing of table names and abbreviations, see paragraph 7.4.)


Interdisciplinary Numbers

11.8 The first class number displayed in an index entry (the unindented term) is the
number for interdisciplinary works. If the term also appears in a table, the table
number is listed next, followed by other aspects of the term. The discipline of the
interdisciplinary number may be repeated as a subentry if the discipline is not clear.
For example:

Adult education 374
T1 —0715
federal aid 379.121 5
law 344.074
public administrative support 353.84
public support 379.114
law 344.076 85
special education 371.904 75
university extension 378.175

11.9 Interdisciplinary numbers are not provided for all topics in the Relative Index. They
are omitted when the index entry is ambiguous, does not have a disciplinary focus, or
lacks literary warrant. In such cases, there is no number opposite the unindented entry.
For example:

blood 573.159
human physiology 612.115
physiology 573.159
water supply treatment 628.162 2

(For more information on interdisciplinary numbers, see paragraphs 5.8, 7.17,
7.20 - 7.21.)

Terms Included in the Relative Index

11.10 The Relative Index contains most terms found in the headings and notes of the
schedules and tables, and synonyms and terms with literary warrant for concepts

represented by the schedules and tables. The Relative Index also contains terms for
the broad concepts covered in Manual notes.

Inverted phrases are avoided, except for personal and geographic names (see
paragraphs 11.12 - 11.13). Qualifiers are used for homonyms, ambiguous terms, and
most initialisms and abbreviations. The most common use of the term may not be
qualified. Disciplinary qualifiers are avoided.

11.11 The following types of names from Table 2 Geographic Areas are included in the
Relative Index: (A) names of countries; (B) names of the states and provinces of most
countries; (C) names of the counties of the United States; (D) names of capital cities and
other important municipalities; and (E) names of certain important geographic features.

11.12 Also included in the Relative Index are the personal names of the following groups of
persons: heads of state used to identify historical periods, e.g., Louis XIV; founders
or revealers of religions, e.g., Muhammad; initiators of schools of thought when used
to identify the school, e.g., Smith, Adam.

11.13 Place names and other proper names are generally given in the form specified by the
second edition, 2002 revision, of the Anglo-American Cataloguing Rules (AACR2),
based on the names established in the Library of Congress authority files. If the AACR2
form is not the common English name, an entry is also included under the familiar
form of the name.

Plants and animals are indexed under their scientific and common names.

11.14 The choice of singular form versus plural form follows ISO 999:1996,
Guidelines for the content, organization and presentation of indexes. Count nouns are
generally in the plural; noncount nouns and abstract concepts are generally in the
singular. Parts of the body are in the plural only when more than one occurs in a fully
formed organism (e.g., ears, hands, nose). Plants and animals follow scientific
convention in choice of singular form versus plural form, with the decision based on
whether the taxonomic class has more than one member (e.g., Horses, Lion, Lipizzaner
horse). Where usage varies across disciplines, the index entry reflects the form preferred
in the discipline where interdisciplinary works are classified.

Terms Not Included in the Relative Index

11.15 Terms usually not included in the Relative Index are:

(A) Phrases beginning with the adjectival form of countries, languages,
nationalities, religions, e.g., English poetry, French cooking, Italian
architecture, Hindu prayer books.

(B) Phrases that contain general concepts represented by standard subdivisions
such as education, statistics, laboratories, and management; e.g., Art
education, Educational statistics, Medical laboratories, Bank management.

When there is strong literary warrant for such a phrase heading as a sought term, it
may be included in the Relative Index, e.g., English literature. When the phrase
heading is a proper name or provides the only form of access to the topic, it may also
be included, e.g., English Channel, French horns, Amharic literature.


12.1 Some devices are required to enable the DDC to serve needs beyond those
represented in the standard English-language edition. At a number of places in the
schedules and tables, options are provided to give emphasis to an aspect in a
library's collection not given preferred treatment in the standard notation. In some
cases, options are also suggested to provide shorter notation for the aspect.

12.2 Options are provided throughout the Classification to emphasize jurisdiction,
ethnic or national group, language, topic, or other characteristic.

12.3 Options described in notes appear in parentheses and begin with "Option:". Options
that apply to the full entry appear at the end of the entry; options to a specific
instruction in the entry are indented under the appropriate note. For example, the
following option appears at the end of the entry for 420 - 490:

(Option B: To give local emphasis and a shorter number to a specific
language, place it first by use of a letter or other symbol, e.g., Arabic
language 4A0 [preceding 420], for which the base number is 4A. Option A is
described under 410)

12.4 Some optional numbers are enumerated in the schedules and tables and appear in

12.5 parentheses in the number column. A special optional arrangement (222) - (224) for
books of the Bible as arranged in Tanakh appears as a subsection of the Manual note
for 221.

12.5 Arrange-alphabetically and arrange-chronologically notes are not placed in
parentheses, but are also options. They represent suggestions only; the material need
not be arranged alphabetically or chronologically. An example of an arrange-
alphabetically note is found at 005.133 Specific programming languages: "Arrange
alphabetically by name of programming language, e.g., C++."

12.6 Some national libraries and central cataloging authorities assign a few optional
numbers, e.g., the National Library of Canada uses C810 for Canadian literature in
English and C840 for Canadian literature in French.

12.7 Most of the time, the responsibility for implementing an option rests with
the local library. Libraries should weigh the value of using an option against the loss
in interoperability of numbers. The library will not be able to use numbers assigned by
other libraries, and other libraries will not be able to use the optional numbers. In
addition, unless the option is widely used in a region, users may be confused by the
alternate notation.

Close and Broad Classification

13.1 The Dewey Decimal Classification provides the basic option of close versus broad
classification. Close classification means that the content of a work is specified by
notation to the fullest extent possible. Broad classification means that the work is
placed in a broad class by use of notation that has been logically abridged. For
example, a work on French cooking is classed closely at 641.5944 (641.59 Cooking
by place + 44 France from Table 2), or broadly at 641.5 (Cooking).

13.2 A library should base its decision on close versus broad classification on the size of
its collection and the needs of its users. For example, a work on the sociology of sibling
relationships in Canadian society would be most usefully classed in 306.8750971
(306.875 Sibling relationships + 09 Geographic treatment from Table 1 + 71 Canada
from Table 2) in a research library or large public library. A small school library might
prefer to class the same work in the broader number (306.875) without including the
geographic facet in the notation. An engineering library might prefer close classification

for works in engineering, but broad classification for disciplines outside science and

13.3 The classifier should never reduce the notation to less than the most specific
three-digit number (no matter how small the library's collection). A number also must
never be reduced so that it ends in a 0 anywhere to the right of the decimal point.

13.4 One aid to logical abridgment of DDC numbers is the segmentation device provided
by the Decimal Classification Division of the Library of Congress and some other
centralized cataloging services.

13.5 The abridged edition of the Dewey Decimal Classification is another source for broad
classification. It is intended for libraries with collections of 20,000 volumes or less.

More Information

14.1 Classifiers desiring a more in-depth introduction to the Dewey Decimal Classification
may consult Dewey Decimal Classification: A Practical Guide, 3d ed., by Lois Mai
Chan and Joan S. Mitchell (Dublin, Ohio: OCLC, 2003).

All copyright rights in the Dewey Decimal Classification system are owned by OCLC.
Dewey, Dewey Decimal Classification, DDC, Forest Press, and OCLC are registered
trademarks of OCLC.

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