The essential components of a scheme of library classification are: 

1. Notation – It is a set of symbols which stands for a class or a subject e.g. philosophy and literature and its sub-division example ethics, English literature representing a scheme of classification. For the purpose of arranging books, use of names of the subjects, broad or specific in natural language would neither be practicable nor convenient so these are translated into artificial language of ordinal numbers. A Notation is of two types, pure or mixed. Only one species of symbols are used in 145 pure notation, either numerals such as 1 to 9 or from letters A to Z. In a mixed notation more than one set of symbols are used. Pure notation is easy to understand but mixed notation is easier to remember and increases the capacity of the scheme of library classification. 

 2. Form Division – Knowledge may be presented in one form of the other, the form could be text book, manual, history, dictionary and encyclopedia. These forms or styles of presenting knowledge of a subject could be commonly applied to any subject. Book classification takes care of representing form in the Call Number (A number by which a book is called for particularly a closed access library). The numbers representing the forms of books are called form divisions. They are also known as common sub-divisions or common-isolates. 

 3. Generalia Class – There are certain books such as encyclopedias, bibliographies and collected writings of an author which cannot be classified under any specific subject since they cover all subjects under the sun and hence are classified under the Generalia Class. 

 4. Index – Index is an essential component of a scheme of Library Classification which is provided at the end of the scheme. It is of immense value to the members in their handling of a classified part of the catalogue. 

 5. Call Number – In classifying, each book is provided with a distinguished number specified to it which can be used for calling the book from the stats and replacing it on its return to its right place. It is known as a Call Number. This Call Number fixes the position of a book or any document in a sequence and helps to locate it through its entry in the catalogue. Each document has its own individual call number which comprises of class numbers which represents the thought content of the book and the book number which represents one or more of the following: Author No., Year of Publication, Accession No. or any other such appropriate feature.

Reference: 

shodhganga.inflibnet.ac.in