The ACM Computing Classification System (CCS) is a subject classification system for computing devised by the Association for Computing Machinery (ACM). The system is comparable to the Mathematics Subject Classification (MSC) in scope, aims, and structure, being used by the various ACM journals to organize subjects by area. History The system has gone through seven revisions, the first version being published in 1964, and revised versions appearing in 1982, 1983, 1987, 1991, 1998, and the now current version in 2012. Structure It is hierarchically structured in four levels. For example, one branch of the hierarchy contains: Computing methodologies Artificial intelligence Knowledge representation and reasoning Ontology engineering See also Computer Science Ontology Physics and Astronomy Classification Scheme arXiv, a preprint server allowing submitted papers to be classified using the ACM CCS Physics Subject Headings References . . . External links dl.acm.org/ccs is the homepage of the system, including links to four complete versions of the system: the 1964 version the 1991 version the 1998 version the current 2012 version. The ACM Computing Research Repository uses a classification scheme that is much coarser than the ACM subject classification, and does not cover all areas of CS, but is intended to better cover active areas of research. In addition, papers in this repository are classified according to the ACM subject classification. Computing Classification System Classification systems Computer science literature 1964 in computing Computer-related introductions in 1964 Computing Classification System