The ICS serves as a structure for catalogues and databases of technical standards and other normative documents, and as a basis for standing-order systems for international, regional and national standards.
Classification principles
The ICS uses an hierarchical classification, which consists of three nested levels called fields, groups and sub-groups. Each field is subdivided into groups, which are further divided into sub-groups. All classification levels are designated by a classification code and a title. The notation is a set of Arabic numerals. Top-level items, which have no parent levels, use a two-digit notation, for example: The notations for groups and sub-groups include the parent-level notations. The example below shows a notation for Sub-Group 20, which belongs to Group 040 in Field 43.
Level 1 (Fields)
A field is the first level in the International Classification for Standards. It may represent one or a combination of the following:
Sub-groups are used in the ICS to subdivide groups into subjects that certain to a particular aspect of the subject covered by a given group. Regardless of the subject, virtually all groups include a sub-group No. 01 that covers the complete subject of the respective group. In addition, most of the groups contain a sub-group No. 99 for standards on subjects which do not correspond either to the subjects of the general sub-groups or to the subjects of the specific sub-groups of the respective groups.
Level 4 subdivisions are not part of the official ICS document. The ICS rules however allow users of the classification system to subdivide the official ICS sub-groups into so-called units, making them a Level 4 component of the International Classification for Standards. This is accomplished by adding a two-digit number to the notation of the sub-group being subdivided. However, instead of a period, new notations use a hyphen as a separator. For example:
Statistics
The International Classification for Standards has 99 top-level divisions of which only 40 are presently used. The remaining 59 divisions are reserved for topics that are not yet known.
There are three "official" levels in the ICS system, each holding ninety nine, nine hundred and ninety nine and ninety nine subsets, respectively.
Each field of the ICS is designed to hold a maximum of 999 groups.
Although any group in the ICS may contain no more than 99 "official" sub-groups, the holding capacity of the group can be expanded 99 times by using "unofficial" Level 4 subdivisions, an option that is built into the ICS. Adding Level 4 subdivisions to all sub-groups within a group increases the group's holding capacity to 9 801 subjects.
The expanded version of the International Classification for Standards is capable of covering nearly 1 billion subjects. This can be achieved without any restructuring of its numerical coding system. Since there are currently about 780 000 national standards in the world, the number of subjects that the ICS can offer for classification purposes exceeds 1 200 times the total number of documents that are available for classification.
