Disciplines and Subjects - Library management:

In a modern library the arrangement of documents is usually by subject. Thus, subject is the characteristic of division for arrangement, of books. A Subject is a systematised, homogeneous and cohesive group of thought or a chunk of knowledge whose depth and breadth are comfortably within the intellectual competence and; the field of specialisation: of a normal intellectual person. But in library classification we are mostly concerned with what is known as a specific subject. A specific subject is always in the context of a. document. A specific subject of a document is defined as the subject of the document "whose extension (scope/breadth) and intension (depth/specificity) are equal to the thought content of the document.  

Knowledge has been divided into major areas called Disciplines. 

A Discipline is a major continuous area, of knowledge formed on the basis of either the similarity of the objects of study (i.e., whether natural objectives, or social issues); or, obtained by a similar mode of study or method of acquiring knowledge (i.e., whether imaginative, or empirical). Broadly speaking there are three major disciplines of the universe of knowledge: 

Sciences (study of natural objects) 

Social Sciences (problems of society)  

Humanities (by imagination/perceptions) 

However, connotations of a discipline vary from time to time. Nowadays all classifications are by disciplines - a breakthrough made by Melvil Dewey (1851-1931). A topic may fall under various disciplines. 

Disciplines are further divided into basic subjects or main classes. A main class is, conventional but very cohesive area of knowledge. In library classification it is more or lens the first line of division of the universe of knowledge. A traditional subdivision of an old main class is known as a Canonical Class. For example, heat, light, magnetism, electricity are canonical classes of the main class physics. Similarly algebra, geometry, analysis are canonical classes of the main class mathematics. Obviously the canonical classes are only of an ancient or traditional main class. A new main class such as library science, journalism, computer science does not have canonical classes. Main classes expounded from a school of thought; say Marxian economics, or Newtonian physics or Homeopathy medicine, are known as System Main Classes. A main class studied from a specialised viewpoint, say aviation medicine, child medicine, sports medicine, or small scale economy are known as Special Main Class. Similarly a main class expounded from a physical or social milieu or environment is known. as Environmental Main Class. For example, war economy, high altitude engineering, tropical medicine are examples of environmental main classes. Main classes as such, canonical, systems, special and environmental main classes, when taken together, are known as Basic Subjects.