Universe of subjects as mapped in different schemes of classification.

The concept of the Universe of Subjects (UoS), often referred to as the Universe of Knowledge (UoK), and how it is mapped, is central to classification theory. Classification aims to depict the structure of knowledge.

The mapping of the UoS involves transforming the inherent multi-dimensional nature of knowledge into a manageable, one-dimensional arrangement, which is the foundational and perennial problem faced by classification designers.

Here is how the Universe of Subjects is mapped in different classification schemes, focusing on major schemes:

I. General Mapping Approaches

The goal of all classification work is to make sense out of chaos by grouping similar things together and ordering the fields of knowledge in a systematic way. Classification systems achieve this mapping by dividing the UoS based on different methodologies:

1. Enumerative Classification Schemes (e.g., LCC, early DDC): These schemes attempt to list or enumerate all possible classes—basic, compound, and often complex subjects—along with predefined class numbers. The classification is presented essentially as a single long schedule.
2. Faceted/Analytico-Synthetic Classification Schemes (e.g., CC, modern UDC): These schemes do not list every subject combination readymade. Instead, they map the UoS by providing schedules of basic classes and isolate ideas (facets), along with a set of rules (grammar) for analyzing a complex subject into its components and synthesizing a unique class number.

II. Mapping in Major Classification Schemes

A. Dewey Decimal Classification (DDC)

DDC, originally published in 1876, is characterized as an almost-enumerative classification.

1. Structure and Scope: DDC attempts to organize the entire domain of knowledge into ten main classes. These ten main classes are hierarchically subdivided into 100 divisions and 1,000 sections.
2. Hierarchical and Numerical Mapping: DDC uses a purely numerical notation (Arabic numerals 0-9) to represent classes. The structure is infinitely hierarchical, with further divisions following a decimal point.
3. Discipline-Oriented Order: DDC is a discipline-oriented classification. Its main classes (000-900) are mapped based on academic disciplines, such as 500 for Natural Sciences and Mathematics, and 300 for Social Sciences.
4. Flexibility (Modern Editions): Though devised as an enumerative scheme, subsequent revisions, particularly since the 18th edition, have absorbed the structure and methodology of faceted classification. It utilizes seven Auxiliary Tables for greater subject specificity, allowing for a limited degree of synthesis (e.g., Geographical/Area Table, Standard Subdivisions).

DDC's structure means that subjects close to each other in a dictionary catalog may be dispersed in the Dewey schedules (e.g., architecture of Chicago separate from geography of Chicago).

B. Library of Congress Classification (LCC)

LCC is described as a purely enumerative classification and is the bulkiest of all systems.

1. Structure and Scope: LCC consists of 21 main classes (in 29 parts and 45 volumes), denoted by single capital letters. It divides these classes into subclasses (double or triple capital letters).
2. Basis (Literary Warrant): LCC's classification structure was developed based mainly on the idea of literary warrant—classes were added only when needed for works owned by the Library of Congress. This approach allowed LCC to incorporate changes and additions of new branches of knowledge easily.
3. Notation and Hierarchy: LCC uses a mixed notation of letters and numerals. Unlike DDC, its numerals (1-9999) occupy a fixed length, meaning they do not always strictly have a positional function to indicate hierarchy. LCC is generally considered less flexible than faceted systems like CC and UDC.

LCC is described as suitable for shelf arrangement and a "mark and park system".

C. Universal Decimal Classification (UDC)

UDC is based on DDC but is considered an improvement that incorporates faceted (analytic-synthetic) elements.

1. Structure and Scope: UDC borrowed its basic structure from DDC, though it merged main classes 4 and 8 (Language and Literature), leaving Main Class 4 vacant.
2. Faceted and Multidimensional Mapping: UDC is basically enumerative but is considered a faceted scheme due to its practice of identifying common characteristics and listing them in auxiliary tables. Its "auxiliary apparatus of relations and synthesis is quite powerful," making it a truly multidimensional scheme capable of specifying minute subjects and their relationships.
3. Auxiliaries and Synthesis: UDC utilizes extensive common auxiliaries (e.g., signs indicating relationships, and subdivisions for space and time) and special auxiliaries. These auxiliaries facilitate synthesis (number building) and the accommodation of new subjects.

D. Colon Classification (CC)

CC, designed by S.R. Ranganathan (first published 1933), is the prime example of a Freely Faceted Analytico-Synthetic Classification.

1. Structure and Order: CC divides the entire domain of knowledge into main classes (27 divisions), arranged in the order of their evolution as academic studies: Science/Technology, Humanities, and Social Sciences. Within each discipline, the main classes are arranged in the order of increasing concreteness based on the principle of dependency.
2. Facet Analysis (PMEST): The mapping is performed through facet analysis, postulating that every subject can be analyzed into components manifested by the Five Fundamental Categories (PMEST): Personality, Matter, Energy, Space, and Time. These categories determine the internal sequence of ideas within a subject.
3. Notational Mapping: CC employs a highly mixed notation using Indo-Arabic numerals, Roman letters (both uppercase and lowercase), Greek letters, and numerous punctuation marks (indicator digits like the colon, comma, semi-colon, period, and inverted comma). This complex notation is designed to be highly expressive of the hierarchical and faceted structure derived in the Idea Plane. The use of postulates and principles (like Wall-Picture Principle) guides the sequencing of these facets when creating a class number (a process called linear arrangement or mapping).

CC's ability to create unique, co-extensive class numbers for virtually infinite compound subjects makes its resilience virtually infinite.