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In information science and
ontology Ontology is the philosophical study of existence, being. It is traditionally understood as the subdiscipline of metaphysics focused on the most general features of reality. As one of the most fundamental concepts, being encompasses all of realit ...
, a classification scheme is an arrangement of classes or groups of classes. The activity of developing the schemes bears similarity to
taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...
, but with perhaps a more theoretical bent, as a single classification scheme can be applied over a wide semantic spectrum while taxonomies tend to be devoted to a single topic. In the abstract, the resulting structures are a crucial aspect of
metadata Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive ...
, often represented as a hierarchical structure and accompanied by descriptive information of the classes or groups. Such a classification scheme is intended to be used for the
classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...
of individual objects into the classes or groups, and the classes or groups are based on characteristics which the objects (members) have in common. The
ISO/IEC 11179 The ISO/IEC 11179 metadata registry (MDR) standard is an international International Organization for Standardization, ISO/International Electrotechnical Commission, IEC standard for representing metadata for an organization in a metadata registry ...
metadata registry standard uses classification schemes as a way to classify administered items, such as
data element In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has: # An identification such as a data element name # A clear data element definition # One or more representation term ...
s, in a
metadata registry A metadata registry is a central location in an organization where metadata definitions are stored and maintained in a controlled method. A metadata repository is the database where metadata is stored. The registry also adds relationships with ...
. Some quality criteria for classification schemes are: * Whether different kinds are grouped together. In other words, whether it is a grouping system or a pure classification system. In case of grouping, a subset (subgroup) does not have (inherit) all the characteristics of the superset, which makes that the knowledge and requirements about the superset are not applicable for the members of the subset. * Whether the classes have overlaps. * Whether subordinates (may) have multiple superordinates. Some classification schemes allow that a kind of thing has more than one superordinate others do not. Multiple supertypes for one subtype implies that the subordinate has the combined characteristics of all its superordinates. This is called multiple inheritance (of characteristics from multiple superordinates to their subordinates). * Whether the criteria for belonging to a class or group are well defined. * Whether the kinds of relations between the concepts are made explicit and well defined. * Whether subtype-supertype relations are distinguished from composition relations (part-whole relations) and from object-role relations.


In linguistics

In
linguistics Linguistics is the scientific study of language. The areas of linguistic analysis are syntax (rules governing the structure of sentences), semantics (meaning), Morphology (linguistics), morphology (structure of words), phonetics (speech sounds ...
,
subordinate A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an importan ...
concepts are described as
hyponym Hypernymy and hyponymy are the wikt:Wiktionary:Semantic relations, semantic relations between a generic term (''hypernym'') and a more specific term (''hyponym''). The hypernym is also called a ''supertype'', ''umbrella term'', or ''blanket term ...
s of their respective superordinates; typically, a hyponym is 'a kind of' its superordinate.Keith Allan (2002, p. 260), Natural Language Semantics, Blackwell Publishers Ltd, Oxford, .


Benefits of using classification schemes

Using one or more classification schemes for the classification of a collection of objects has many benefits. Some of these include: * It allows a user to find an individual object quickly on the basis of its kind or group. * It makes it easier to detect duplicate objects. * It conveys
semantics Semantics is the study of linguistic Meaning (philosophy), meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction betwee ...
(meaning) of an object from the definition of its kind, which meaning is not conveyed by the name of the individual object or its way of spelling. * Knowledge and requirements about a kind of thing can be applied to other objects of that kind.


Kinds of classification schemes

The following are examples of different kinds of classification schemes. This list is in approximate order from informal to more formal: *
thesaurus A thesaurus (: thesauri or thesauruses), sometimes called a synonym dictionary or dictionary of synonyms, is a reference work which arranges words by their meanings (or in simpler terms, a book where one can find different words with similar me ...
– a collection of categorized concepts, denoted by words or phrases, that are related to each other by narrower term, wider term and related term relations. *
taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...
– a formal list of concepts, denoted by controlled words or phrases, arranged from abstract to specific, related by subtype-supertype relations or by superset-subset relations. *
data model A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to the properties of real-world entities. For instance, a data model may specify that the data element representing a car be ...
– an arrangement of concepts (entity types), denoted by words or phrases, that have various kinds of relationships. Typically, but not necessarily, representing requirements and capabilities for a specific scope (application area). * network (mathematics) – an arrangement of objects in a random graph. *
ontology Ontology is the philosophical study of existence, being. It is traditionally understood as the subdiscipline of metaphysics focused on the most general features of reality. As one of the most fundamental concepts, being encompasses all of realit ...
– an arrangement of concepts that are related by various well defined kinds of relations. The arrangement can be visualized in a
directed acyclic graph In mathematics, particularly graph theory, and computer science, a directed acyclic graph (DAG) is a directed graph with no directed cycles. That is, it consists of vertices and edges (also called ''arcs''), with each edge directed from one ...
. One example of a classification scheme for
data element In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has: # An identification such as a data element name # A clear data element definition # One or more representation term ...
s is a
representation term A representation term is a word, or a combination of words, that semantically represent the data type (value domain) of a data element. A representation term is commonly referred to as a ''class word'' by those familiar with data dictionaries. ISO ...
.


See also

*
ISO/IEC 11179 The ISO/IEC 11179 metadata registry (MDR) standard is an international International Organization for Standardization, ISO/International Electrotechnical Commission, IEC standard for representing metadata for an organization in a metadata registry ...
*
Faceted classification A faceted classification is a classification scheme used in organizing knowledge into a systematic order. A faceted classification uses semantic categories, either general or subject-specific, that are combined to create the full classification ...
*
Metadata Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive ...
*
Ontology (computer science) In information science, an ontology encompasses a representation, formal naming, and definitions of the categories, properties, and relations between the concepts, data, or entities that pertain to one, many, or all domains of discourse. More ...
* Representation class *
Representation term A representation term is a word, or a combination of words, that semantically represent the data type (value domain) of a data element. A representation term is commonly referred to as a ''class word'' by those familiar with data dictionaries. ISO ...
* Simple Knowledge Organisation System * Semantic spectrum


References


External links


OECD Glossary of Statistical Terms – Classification Schemes

ISO/IEC 11179-2:2005 Metadata registries (MDR) – Part 2: Classification

Nancy Lawler's presentation on Classification Schemes
{{Webarchive, url=https://web.archive.org/web/20070928151647/http://metadata-standards.org/metadata-stds/Document-library/Meeting-reports/SC32WG2/2002-05-Seoul/WG2-SEL-018%20ISO-IEC-11179-2%20presentation-to-open-forum.ppt , date=2007-09-28 Metadata Metadata registry ISO/IEC 11179 Classification systems