On one extreme, a Library classification scheme can be completely enumerative where every subject and class ID listed with a pre-defined notation and the classifier has simply to choose a class and the corresponding notation. On the other hand, a classification scheme can be fully faceted, where the classifier has to follow a set of rules to construct a class number. In between these two extremes there is also a classification scheme that to some extent is enumerative but also makes provision for some sort of synthesis to build the class number. These are called analytico-synthetic classification schemes.

Enumerative Classification Schemes: DDC
An enumerative Library classification scheme is a scheme where all the possible classes are enumerated according to certain characteristics. There is a top down approach whereby a series of subordinate classes are produced and where both simple and complex subjects are listed. The advantage of this scheme is that the structure of the scheme is shown by the notation as far as practicable. Users can easily find the coordinate and subordinate classes and can make a map of the subject. The disadvantage is that it is difficult to accommodate new subjects and frequent revisions may be required. An enumerative classification scheme, in some cases, displays hierarchical structures of notation. The basic tenet of this scheme is that all the possible subjects and topics are listed along with a predefined class number, and therefore the classifier does not have to create any class number such as Dewey Decimal Classification.

Analytico-Synthetic Classification Scheme
Analytico-Synthetic Library classification schemes resolve some of the problems of enumerative classification schemes. The concept behind this scheme is that the subject of a given document will be divided into its constituent elements and then the classification scheme will be used to find notations for each element, which will then be combined according to the prescribed rules to prepare the final class number. This scheme overcomes the two major problems of enumerative classification schemes as, by providing various tables, specific notational symbols and rules, they avoid the necessity for a long list of classes, and thus produce a smaller classification scheme in size; they also provide flexibility to users as specific numbers can be built and the classifier is not restricted by the availability of a specific subject. Nevertheless, it makes classifiers job complex since they have to construct the class numbers as opposed to just selecting one from a list like Universal Decimal Classification.

Faceted Classification Scheme: Colon Classification
A faceted classification scheme is on the other extreme of the scale since instead of listing of all the classes and the corresponding numbers, it lists the various facets of every subject or main class and provides a set of rules for constructing class numbers through facet analysis. The concept of facet analysis was proposed by Dr. S. R. Ranganathan and was used in his faceted classification scheme called Colon Classification. The basic idea was that any component or facet of a subject can fit into five fundamental categories: Personality, Matter, Energy, Space and Time which became the major focus of classification research from 1930 onwards resulting in to the Colon Classification.

The Universal Decimal Classification (UDC) scheme of classification was developed in the year 1895 by the Belgium Barrister Paul Otlet and Nobel Prize winner Henri La Fountaine. The UDC is peculiar in the sense that it consists of a combination of both enumerative and faceted character of the schemes and hence it is designated as an Almost-Faceted Scheme of Classification. The UDC is derived from DDC as universal since it encompasses the whole field of knowledge. It is the multi-lingual general classification tool for organizing all kinds of recorded knowledge in the library. It is an international classification system mainly developed for the purpose of indexing and arranging an enormous card bibliography which not only includes books but also all kinds of documents, periodical articles, patents, trade catalogues, abstracts and other micro documents in more than 28 different international languages.

The International Institute of Bibliography (IIB) was organized under the aegis of an International Conference on Bibliography held in Brussels in 1895. One of the main objectives was to devise a scheme of classification for its use in indexing world literature. The existing schemes of classification were found inadequate for the purpose therefore; it is an international extension and adaptation of the DDC, initially by two Belgians, Paul Otlet and Henry La Fontaine. The first edition appeared in French in 1905 as Manuel du Repertoire Bibliographique Universel, which has 33,000 sub-divisions. The second edition was also published in French containing 70,000 sub-divisions. The third edition was published in German in 7 volumes of tables and 3 volumes of alphabetic index containing 140,000 sub-divisions. Full editions have also appeared in French, Spanish and Japanese languages. The publication of the English translation was started in 1943 entitled, “Universal Decimal Classification” and was designated as the fourth international edition. The British Standards Institution published the third revised edition of the abridged English Edition in 1961. The Abridged edition of the UDC has been published in 13 different languages.

Purpose of UDC:
UDC is designed to serve the following purposes:

• To provide a method for arranging books on library shelves in an order which would be helpful to the users i.e. shelf arrangement.
• To provide a method of arranging sub-titles of the books themselves in a catalogue and printed bibliographies.
• To classify the recorded knowledge.
• To retrieve the document or locate the document.

Features of UDC:
UDC has following features:

• UDC is a practical scheme based on the demands of pamphlets, reports and periodical literature rather than the framework of a theory.
• The scheme is based on DDC and claims to be the first Analytico-synthetic classification scheme.
• It lays more stress to achieve co-extensive class numbers i.e. detailed specification than the achievement of a sequence of subjects for optimum helpfulness.
• It avoids the lacunae of numerous private classification schemes by providing a standard system covering all the disciplines and may be used in any type of library.
• It is a general classification scheme and not a bundle of special classification. It is rather an integrated whole.
• The scheme reflects exhaustive enumeration in the schedule with due provision for synthesis or coordination.
• It is amenable to adjustments to meet the special needs because a citation order in any given class allows alternative treatment.
• The use of synthetic devices like colon (:), permits coordination of concept in different permutation, there by minimizing the rigidity in the enumerated classification scheme.
• An International body for its maintenance and revision with full cooperation of its users guarantees the continual existence of the system as a current and up-to-date one.
• The terminology used in UDC helps in a comprehensive vocabulary of terms for indexing purposes.

Principles of UDC:
It is a classification in the strict sense depending on the analysis of idea content, so that the related concepts and groups of concepts are brought together and are arbitrary or haphazard systemization of alphabetical and other arrangements are avoided. It is a universal classification system for which an attempt has been made to include in it every field of knowledge not as a patch work of isolates, self-sufficient specialists grouping but as an integrated pattern and correlated subjects. It is constructed on the principals of proceeding from general to the more particular revision of the whole human knowledge into ten main branches each further sub-divided decimally to the required degree. It is a practical system for retrieval of information in which the order of subjects is not of much importance than the provision for detailed specifications. It also accepts the principles of mutually exclusive classes, collection of related subjects and consistency of approach. It has tried to remove national and racial basis to some extent by removing these factors and performing common facets. Its notation consists of Indo-Arabic numerals used decimally which allows infinite hospitality and social sciences. It employs certain notational techniques by which it is possible to link simple main class either which other main number with auxiliaries indicating place, time and similar commands used for categories.

UDC Notations and Symbols:
The UDC is based on the outline and the notational base of the Dewey Decimal Classification. The basic notation of UDC consists of Indo-Arabic numerals 0-9 used decimally, the different mathematical symbols and punctuation marks that have converted its notation into a mixed notation. The naught and decimal point have been omitted for convenience and have been implied. The numbers are simply indicated that is 0, 1, 2, 3, 4, 5—-. UDC uses single digit numbers and every digit is a significant one. However, the use of different signs and symbols has added qualities to the notation of UDC.

Structure of UDC:
The whole universe of knowledge in UDC is divided into two categories: Systematic Tables (Schedules) which give the notational number of all basic class from 0-9. The general order and nomenclature of the main table is the same as DDC. The whole universe of knowledge is divided into ten main branches denoted by decimal fractions, Indo-Arabic numerals. UDC uses one-digit numbers for the main class. The main class numbers and their subdivisions are divided by a continuous extension of the decimal fraction on the principle of proceeding from general to specific. The practice of DDC to use a dot after every three digits has been retained in UDC. In UDC, the 4th class is kept vacant for future subjects.

Ten main Class of UDC:

• 0 Science and Knowledge. Organization. Computer Science. Information Science. Documentation. Librarianship. Institutions. Publications
• 1 Philosophy. Psychology
• 2 Religion. Theology
• 3 Social Sciences
• 4 Vacant
• 5 Mathematics. Natural Sciences
• 6 Applied Sciences. Medicine, Technology
• 7 The Arts. Entertainment. Sport
• 8 Linguistics. Literature
• 9 Geography. History

Revision Policy of UDC:
The Scheme is revised and updated from time to time by the International Federation for Information and Documentation (FID). The development and maintenance of UDC is achieved by FID at Hague through its ultimate coordinating body i.e. Central Classification Committee. This committee is assisted in its work, directly or indirectly by the National Committees, Special Subject Committees in each Country and International Subject Committees. Thus, it follows a decentralized procedure for revision of the UDC. The revision is done in the following three ways: Extension of topics by more detailed sub-divisions; Minor changes in the existing class numbers of sub-divisions; Starvation Policy introduced by Donker Duyvis. This policy assumes a fairly state of collection and opportunity for re-classification. Donker Duyvis used the unused notation in the dynamic and rapidly changing subject. If the users of the UDC want to suggest amendments or extensions to the schedules, they have to suggest the same to a National Body in their respective Countries. The changes in the UDC are communicated to its users by a half-yearly bulletin titles Extensions and Corrections to UDC. From the end of 1991 responsibility and updating was assumed by a new organization, the UDC Consortium (UDCC) who publishes the bulletin, Extensions and Corrections of the UDC.

The Dewey Decimal Classification (DDC), colloquially the Dewey Decimal System, is a proprietary library classification system first published in the United States by Melvil Dewey in 1876. Originally described in a four-page pamphlet, it has been expanded to multiple volumes and revised through 23 major editions, the latest printed in 2011. It is also available in an abridged version suitable for smaller libraries. OCLC, a non-profit cooperative that serves libraries, currently maintains the system and licenses online access to WebDewey, a continuously updated version for catalogers.

The Decimal Classification introduced the concepts of relative location and relative index which allow new books to be added to a library in their appropriate location based on subject. Libraries previously had given books permanent shelf locations that were related to the order of acquisition rather than topic. The classification’s notation makes use of three-digit Arabic numerals for main classes, with fractional decimals allowing expansion for further detail. Using Arabic numerals for symbols, it is flexible to the degree that numbers can be expanded in linear fashion to cover special aspects of general subjects. A library assigns a classification number that unambiguously locates a particular volume in a position relative to other books in the library, on the basis of its subject. The number makes it possible to find any book and to return it to its proper place on the library shelves. The classification system is used in 200,000 libraries in at least 135 countries.

Administration and publication
Dewey and a small editorial staff managed the administration of the very early editions. Beginning in 1922, the Lake Placid Club Educational Foundation, a not-for-profit organization founded by Melvil Dewey, managed administrative affairs. The ALA set up a Special Advisory Committee on the Decimal Classification as part of the Cataloging and Classification division of ALA in 1952. The previous Decimal Classification Committee was changed to the Decimal Classification Editorial Policy Committee, with participation of the ALA Division of Cataloging and Classification, and of the Library of Congress.

Melvil Dewey edited the first three editions of the classification system and oversaw the revisions of all editions until his death in 1931. May Seymour became editor in 1891 and served until her death in 1921. She was followed by Dorcas Fellows, who was editor until her death in 1938. Constantin J. Mazney edited the 14th edition. Milton Ferguson functioned as editor from 1949 to 1951. The 16th edition in 1958 was edited under an agreement between the Library of Congress and Forest Press, with David Haykin as director. Editions 16–19 were edited by Benjamin A. Custer and the editor of edition 20 was John P. Comaromi. Joan Mitchell was editor until 2013, covering editions 21 to 23. In 2013 Michael Panzer of OCLC became Editor-in-Chief. The Dewey Editorial Program Manager since 2016 has been Dr. Rebecca Green.

Dewey himself held copyright in editions 1 to 6 (1876–1919). Copyright in editions 7–10 was held by the publisher, The Library Bureau. On the death of May Seymour, Dewey conveyed the “copyrights and control of all editions” to the Lake Placid Club Educational Foundation, a non-profit chartered in 1922. The Online Computer Library Center (OCLC) of Dublin, Ohio, US, acquired the trademark and copyrights associated with the Dewey Decimal Classification system when it bought Forest Press in 1988. In 2003 the Dewey Decimal Classification came to the attention of the U.S. press when OCLC sued the Library Hotel for trademark infringement for using the classification system as the hotel theme. The case was settled shortly thereafter.

The OCLC has maintained the classification since 1988, and also publishes new editions of the system. The editorial staff responsible for updates is based partly at the Library of Congress and partly at OCLC. Their work is reviewed by the Decimal Classification Editorial Policy Committee, a ten-member international board which meets twice each year. The four-volume unabridged edition was published approximately every six years, with the last edition (DDC 23) published in mid-2011. In 2017 the editorial staff announced that the English edition of DDC will no longer be printed, in favor of using the frequently updated WebDewey. An experimental version of Dewey in RDF was previously available at dewey.info beginning in 2009, but has not been available since 2015.

In addition to the full version, a single-volume abridged edition designed for libraries with 20,000 titles or fewer has been made available since 1895. The last printed English abridged edition, Abridged Edition 15, was published in early 2012.

Design
The Dewey Decimal Classification organizes library materials by discipline or field of study. Main divisions include philosophy, social sciences, science, technology, and history. The scheme comprises ten classes, each divided into ten divisions, each having ten sections. The system’s notation uses Arabic numbers, with three whole numbers making up the main classes and sub-classes and decimals designating further divisions. The classification structure is hierarchical and the notation follows the same hierarchy. Libraries not needing the full level of detail of the classification can trim right-most decimal digits from the class number to obtain more general classifications. For example: 500 Natural sciences and mathematics; 510 Mathematics; 516 Geometry; 516.3 Analytic geometries; 516.37 Metric differential geometries; 516.375 Finsler geometry.

The classification was originally enumerative, meaning that it listed all of the classes explicitly in the schedules. Over time it added some aspects of a faceted classification scheme, allowing classifiers to construct a number by combining a class number for a topic with an entry from a separate table. Tables cover commonly-used elements such as geographical and temporal aspects, language, and bibliographic forms. For example, a class number could be constructed using 330 for economics + .9 for geographic treatment + .04 for Europe to create the class 330.94 European economy. Or one could combine the class 973 (for the United States) + .05 (for periodical publications on the topic) to arrive at the number 973.05 for periodicals concerning the United States generally. The classification also makes use of mnemonics in some areas, such that the number 5 represents the country Italy in classification numbers like 945 (history of Italy), 450 (Italian language), 195 (Italian philosophy). The combination of faceting and mnemonics makes the classification synthetic in nature, with meaning built into parts of the classification number.

The Dewey Decimal Classification has a number for all subjects, including fiction, although many libraries maintain a separate fiction section shelved by alphabetical order of the author’s surname. Each assigned number consists of two parts: a class number (from the Dewey system) and a book number, which “prevents confusion of different books on the same subject”. A common form of the book number is called a Cutter number, which represents the author and distinguishes the book from other books on the same topic.

Library classification schemes are tools that allow us to allocate a class mark an artificial notation comprising alphanumeric characters and punctuation marks to every item based on its subject content so that the library staff can preserve all the related items together on the library shelves. They are the logical arrangements of subjects plus a system of symbols representing those subjects. Classification schemes aid a classifier to represent the subject content of every document by appropriate notations.

Comparative Study of Three Major Schemes of Classification:

Authorship confers credit and has important academic, social, and financial implications. Authorship also implies responsibility and accountability for published work. The following recommendations are intended to ensure that contributors who have made substantive intellectual contributions to a paper are given credit as authors, but also that contributors credited as authors understand their role in taking responsibility and being accountable for what is published.

Because authorship does not communicate what contributions qualified an individual to be an author, some journals now request and publish information about the contributions of each person named as having participated in a submitted study, at least for original research. Editors are strongly encouraged to develop and implement a contributorship policy. Such policies remove much of the ambiguity surrounding contributions, but leave unresolved the question of the quantity and quality of contribution that qualify an individual for authorship. The ICMJE has thus developed criteria for authorship that can be used by all journals, including those that distinguish authors from other contributors.

Who Is an Author?
The ICMJE recommends that authorship be based on the following 4 criteria:

1. Substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; AND
2. Drafting the work or revising it critically for important intellectual content; AND
3. Final approval of the version to be published; AND
4. Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

In addition to being accountable for the parts of the work he or she has done, an author should be able to identify which co-authors are responsible for specific other parts of the work. In addition, authors should have confidence in the integrity of the contributions of their co-authors.

All those designated as authors should meet all four criteria for authorship, and all who meet the four criteria should be identified as authors. Those who do not meet all four criteria should be acknowledged—see Section II.A.3 below. These authorship criteria are intended to reserve the status of authorship for those who deserve credit and can take responsibility for the work. The criteria are not intended for use as a means to disqualify colleagues from authorship who otherwise meet authorship criteria by denying them the opportunity to meet criterion #s 2 or 3. Therefore, all individuals who meet the first criterion should have the opportunity to participate in the review, drafting, and final approval of the manuscript.

The individuals who conduct the work are responsible for identifying who meets these criteria and ideally should do so when planning the work, making modifications as appropriate as the work progresses. We encourage collaboration and co-authorship with colleagues in the locations where the research is conducted. It is the collective responsibility of the authors, not the journal to which the work is submitted, to determine that all people named as authors meet all four criteria; it is not the role of journal editors to determine who qualifies or does not qualify for authorship or to arbitrate authorship conflicts. If agreement cannot be reached about who qualifies for authorship, the institution(s) where the work was performed, not the journal editor, should be asked to investigate. If authors request removal or addition of an author after manuscript submission or publication, journal editors should seek an explanation and signed statement of agreement for the requested change from all listed authors and from the author to be removed or added.

When a large multi-author group has conducted the work, the group ideally should decide who will be an author before the work is started and confirm who is an author before submitting the manuscript for publication. All members of the group named as authors should meet all four criteria for authorship, including approval of the final manuscript, and they should be able to take public responsibility for the work and should have full confidence in the accuracy and integrity of the work of other group authors. They will also be expected as individuals to complete conflict-of-interest disclosure forms.

Non-Author Contributors
Contributors who meet fewer than all 4 of the above criteria for authorship should not be listed as authors, but they should be acknowledged. Examples of activities that alone (without other contributions) do not qualify a contributor for authorship are acquisition of funding; general supervision of a research group or general administrative support; and writing assistance, technical editing, language editing, and proofreading. Those whose contributions do not justify authorship may be acknowledged individually or together as a group under a single heading (e.g. “Clinical Investigators” or “Participating Investigators”), and their contributions should be specified (e.g., “served as scientific advisors,” “critically reviewed the study proposal,” “collected data,” “provided and cared for study patients”, “participated in writing or technical editing of the manuscript”).