Introduction
LCSH stands for Library of Congress Subject heading, which is a list of headings with the most specific word or phrase that describes the subject that comes from a controlled vocabulary. A subject could be a place, an animal, an event, etc. It is produced and proven by a state of authority that is very skilled with the cataloging process. The library of congress submits the proposals to the professional catalogers to deal with the new headings and the changes of old ones to be approved, And the approved proposals become a part of the online authority file of subject heading for the Library of Congress. The titles of subjects varies in fields, such as science, religion , history, education, etc. The main purpose of The Library of Congress Subject Heading is to provide a standardized English subject category terms in order to limit the endless keyword synonyms and variant phrases and foreign language terms. The reading introduces the components of entries, and some of LCSH origins and a brief explanation of its elements with a detailed description of the Compositions, Vocabulary terms, Class numbers, Scope Notes, References and its relationship with headings and the Equivalence Relationship.
History of LCSH
After the relocation of the Library of congress from U.S Capitol into its new building in 1897, they have changed the way they process with subject cataloging by using dictionary catalog instead of alphabetic-classed. during the 100-year period. The library of congress showed indication that an increased willingness on the part of the Library of Congress to involve the larger library community in the creation or revision of subject headings and other decision-making regarding the LCSH system. During the 8th edition , they have changed its name from the Dictionary Catalogues of the Library of Congress into what we know today, Which is the Library of Congress Subject Heading (LCSH). Subject headings and subdivisions get a constant adding, change and removing of subject headings to its list. It is a continuous process that has been going since its first release back in 1898, It used to be in a print format. The current edition is in CR-ROM version in order to support other platforms and schemes such as MARC-21. When it first was created, it was meant to be used only in the library of congress as a vocabulary system, there was no intention for classification system to be used by other libraries.

LCSH main components
One of the Library of Congress Subject Heading main components is the heading, they are also called compositions, which is listed in bold text, and it may consists of one word or several words as in a phrase, one example of a one word, is a noun such as Schools, Teachers, Students etc. Concepts are normally named in the singular and objects in the plural, though exceptions may be found. As for the Two-word headings, it usually contains an adjective and a noun that usually are used in normal word order such as Mechanical engineering, University students etc. or it can also be inverted in order to bring the noun into the initial position, with the first word followed by a coma, such as Cooking, Kuwaiti.
The original objective of LCSH was to follow a dictionary-classed plan instead of an alphabetic-class plan, many headings were constructed in a manner which is to place the name of the class first through the use of subdivision, through inversion or parenthetical qualification, such as Railroads—Tickets, Vehicles— Snow bungee. These examples are commonly used in the list today. As for the Geographical features they words are traditionally get inverted in order to place a significant word in the initial position instead of the generic word. For example Lake Erie which is formulated as Erie, Lake distinguishing it, so it appears first.
As for headings with two words, the heading may include prepositional phrases and conjunctions. Words that many express a reciprocal relationship, such as Science and technology, or other words that might be a combination of two headings that are very similar that it is treated together in one book, such as Bolts and nuts. Two word headings could also be prepositional phrases, that can also be inverted, such as Water, Effects of pollution. Or in normal word form, such as Photography of flowers.
It is also stated that subject headings use class numbers, which is 36 percent of the subject headings in LCSH, which represents the most common aspect of a subject, It also includes an explanatory term to indicate the specific discipline, for example Diesel motor [TJ795]. Class numbers are added when there is a correspondence between the subject heading and the provisions of the Library of Congress classification schedules, Because these, as well as the subject heading list, are subject to continuous revision, the class numbers in the LCSH should not be used without verification in the latest editions of the schedules and their supplements.
References in LCSH
The purpose of using References in LCSH is to link the unauthorized or non-preferred term to an authorized heading, with a code (Used for) under the heading. For example, Cars (Automobiles), it can also be used for the earlier forms of a heading to describe terms that have been altered. They could also be variant spellings, synonyms and variant form of expression. There is also a Hierarchical relationship with broader topics (BT) and narrower topics (NT) subject headings that are linked through cross-references , class member subject headings that are narrow usually come under broader terms, such as Internet television, BT television. As showed in the example they are linked to the subject heading hierarchy. Creating hierarchical relationships clears the complications and misdirects with the system. these headings were applied after 1984, the ones before that are reviewed on a gradual basis. It also creates the ability to find systematically headings that are more specific and general how matter the level of the entry or searching from narrow to broader or broader to narrower.
In The library of Congress Subject Headings there is also associative relationships, one that can be described as related topics to the headings (RT), which relates or links two headings that are associated in some manner by other than hierarchy, such as transportation, RT Commerce. The policy of LCSH states that headings will be linked by associative references until the hierarchy in the list has been thoroughly reviewed. Moreover, general references (SA) on the other hand is made to serve entire groups of headings, not a specific individual headings, and they usually get replaced by specific references to narrower headings.

Types of Subdivisions
Subdivisions comes hand in hand with subject headings. The main purpose of subdivisions is handle complex topics and combine a number of difference concepts into a singular subject heading. Subject headings and subdivisions are separated by a long dash, such as “Transportation—Economic aspects”. There are couple of subdivisions types. Geographical divisions that represents locations like countries and regions, not as a designation Not ( subd Geog), such as “Kuwait—history “. The second one is Form divisions, which is for the material type like dictionaries, periodicals etc. And they are usually used under any topic, such as “Kuwait—history—periodicals”. The third one is Topical divisions for the aspects of the subject in order to limit the concepts expressed by the heading to a special subtopic, such as “Automobiles—Motors—Carburetors“. and the Chronological division which is to specify a particular time frame. It could specify a period of time or a certain century. Such as Philosophy, French—18th century, Art, Chinese—To 221 B.C. And lastly, Free—floating subdivisions, which is assembled in building-block fashion and most of floating subdivisions are accessible in the Library of Congress Subject Heading, each free floating subdivision comes with a scope note that notifies the researcher if the heading is allowed to be assigned for the chosen heading.

Pattern Headings and Categories of Headings
After free-floating subdivisions that is controlled by pattern heading was officially incorporated into LCSH back in the 1974. Pattern Headings has been identified by the library of congress a representation of particular categories. a standardized sets of topical and form subdivisions were developed for use for certain categories of subject headings or names, used for a subject. In order to stop the subdivisions getting repeated in all headings. Therefore, only one representative headings gets printed in LCSH from each category. If an important topic is represented in the category, they, general free-floating topical and subdivisions can come under pattern headings, such as subdivisions that has been developed for organs and regions, such as Artery ;toes. The table of pattern heading is listed in the right hand column in LCSH and it is arranged alphabetically by category of headings. nEver since LCSH was created, it was meant for listing topical subject headings. There are three categories of headings are omitted from the list; headings that appear in the Name Authority File, free- floating phrase headings, and certain music headings.Headings Residing in the Name Authority File. Furthermore, in 1976 the library of congress made decisions to omit some of the headings such as scared books, families, royalties, gods, legends etc. The library also began to print other categories of formerly omitted headings, such as geographic regions and features; city sections. The list also contains an artificial structure called multiple subdivisions, which are intended to indicate the analogous subdivisions that may be used without a specific authority record, such as civil rights—religious aspects.

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