"The Proposed international standard nomenclature for fields of science and technology was proposed in 1973 and 1974 by the Division of Science Policy and Statistics for Science and Technology of UNESCO and adopted by the Scientific Advisory Committee. This is a classification system widely used in knowledge management of research projects and dissertations. Categories are divided into three hierarchical levels: Fields: Refering to general sections. Encoded with two digits and comprises several disciplines. Disciplines: Provide an overview of specialty groups in Science and Technology. Encoded with four digits. Despite being different from each other disciplines with cross references, or within the same field, are considered to have common characteristics. Subdisciplines: Entries are the more specific elements of the nomenclature and represent the activities that take place within a discipline. Encoded with six digits. In turn, must correspond to individual specialties in science and technology."