Taxonomy

Taxonomy is the practice and science of categorization or classification based on discrete sets. The word finds its roots in the Greek language , "taxis" (meaning 'order', 'arrangement') and , "nomos" ('law' or 'science').
A taxonomy (or taxinomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. Among other things, a taxonomy can be used to organize and index knowledge (stored as documents, articles, videos, etc.), such as in the form of a library classification system, or a search engine taxonomy, so that users can more easily find the information they are searching for. Many taxonomies are hierarchies (and thus, have an intrinsic tree structure), but not all are.
Originally, taxonomy referred only to the categorisation of organisms or a particular categorisation of organisms. In a wider, more general sense, it may refer to a categorisation of things or concepts, as well as to the principles underlying such a categorisation. Taxonomy organizes taxonomic units known as "taxa" (singular "taxon").
Taxonomy is different from meronomy, which deals with the categorisation of parts of a whole.
Applications.
Wikipedia categories illustrate a taxonomy, and a full taxonomy of Wikipedia categories can be extracted by automatic means. , it has been shown that a manually-constructed taxonomy, such as that of computational lexicons like WordNet, can be used to improve and restructure the Wikipedia category taxonomy.
In a broader sense, taxonomy also applies to relationship schemes other than parent-child hierarchies, such as network structures. Taxonomies may then include a single child with multi-parents, for example, "Car" might appear with both parents "Vehicle" and "Steel Mechanisms"; to some however, this merely means that 'car' is a part of several different taxonomies. A taxonomy might also simply be organization of kinds of things into groups, or an alphabetical list; here, however, the term vocabulary is more appropriate. In current usage within knowledge management, taxonomies are considered narrower than ontologies since ontologies apply a larger variety of relation types.
Mathematically, a hierarchical taxonomy is a tree structure of classifications for a given set of objects. It is also named containment hierarchy. At the top of this structure is a single classification, the root node, that applies to all objects. Nodes below this root are more specific classifications that apply to subsets of the total set of classified objects. The progress of reasoning proceeds from the general to the more specific.
By contrast, in the context of legal terminology, an open-ended contextual taxonomy is employed—a taxonomy holding only with respect to a specific context. In scenarios taken from the legal domain, a formal account of the open-texture of legal terms is modeled, which suggests varying notions of the "core" and "penumbra" of the meanings of a concept. The progress of reasoning proceeds from the specific to the more general.
History.
Anthropologists have observed that taxes are generally embedded in local stores and social systems, and serve various social functions. Perhaps the most well-known and influential study of folk taxes is Émile Durkheim's "The Elementary Forms of Religious taxes". A more recent treatment of folk taxonomies (including the results of several decades of empirical research) and the discussion of their relation to the scientific taxonomy can be found in Scott Atran's "Cognitive Foundations of Natural History." Folk taxonomies of organisms have been found in large part to agree with scientific classification, at least for the larger and more obvious species, which means that it is not the case that folk taxonomies are based purely on utilitarian characteristics.
In the seventeenth century the German mathematician and philosopher Gottfried Leibniz, following the work of the thirteenth-century Majorcan philosopher Ramon Llull on his "Ars generalis ultima", a system for procedurally generating concepts by combining a fixed set of ideas, sought to develop an alphabet of human thought. Leibniz intended his "characteristica universalis" to be an "algebra" capable of expressing all conceptual thought. The concept of creating such a "universal language" was frequently examined in the 17th century, also notably by the English philosopher John Wilkins in his work "An Essay towards a Real Character and a Philosophical Language" (1668), from which the classification scheme in Roget's Thesaurus ultimately derives.
Taxonomy in various disciplines.
Natural sciences.
Taxonomy in biology encompasses the description, identification, nomenclature, and classification of organisms. Uses of taxonomy include:
Business and economics.
Uses of taxonomy in business and economics include:
Computing.
Software engineering.
Vegas et al. make a compelling case to advance the knowledge in the field of software engineering through the use of taxonomies. Similarly, Ore et al. provide a systematic methodology to approach taxonomy building in software engineering related topics.
Several taxonomies have been proposed in software testing research to classify techniques, tools, concepts and artifacts. The following are some example taxonomies: 
Engström et al. suggest and evaluate the use of a taxonomy to bridge the communication between researchers and practitioners engaged in the area of software testing. They have also developed a web-based tool to facilitate and encourage the use of the taxonomy. The tool and its source code are available for public use.
Education and academia.
Uses of taxonomy in education include:
Safety.
Uses of taxonomy in safety include:
Research publishing.
Citing inadequacies with current practices in listing authors of papers in medical research journals, Drummond Rennie and co-authors called in a 1997 article in "JAMA", the "Journal of the American Medical Association" for 
"a radical conceptual and systematic change, to reflect the realities of multiple authorship and to buttress accountability. We propose dropping the outmoded notion of author in favor of the more useful and realistic one of contributor." 
Since 2012, several major academic and scientific publishing bodies have mounted "Project CRediT" to develop a controlled vocabulary of contributor roles. Known as "CRediT (Contributor Roles Taxonomy)", this is an example of a flat, non-hierarchical taxonomy; however, it does include an optional, broad classification of the degree of contribution: "lead", "equal" or "supporting". Amy Brand and co-authors summarise their intended outcome as:
Identifying specific contributions to published research will lead to appropriate credit, fewer author disputes, and fewer disincentives to collaboration and the sharing of data and code.
As of mid-2018, this taxonomy apparently restricts its scope to "research outputs", specifically journal articles; however, it does rather unusually "hope to … support identification of peer reviewers". (As such, it has not yet defined terms for such roles as editor or author of a chapter in a "book" of research results.) Version 1, established by the first Working Group in the (northern) autumn of 2014, identifies 14 specific contributor roles using the following defined terms:
Reception has been mixed, with several major publishers and journals planning to have implemented CRediT by the end of 2018, whilst almost as many aren't persuaded of the need or value of using it. For example,
The National Academy of Sciences has created a "TACS (Transparency in Author Contributions in Science)" webpage to list the journals that commit to setting authorship standards, defining responsibilities for corresponding authors, requiring ORCID iDs, and adopting the CRediT taxonomy.
The same webpage has a table listing 21 journals (or families of journals), of which:
The taxonomy is an open standard conforming to the OpenStand principles, and is published under a Creative Commons licence.
Taxonomy for the web.
Websites with a well designed taxonomy or hierarchy are easily understood by users, due to the possibility of users developing a mental model of the site structure.
Guidelines for writing taxonomy for the web include:
Is-a and has-a relationships, and hyponymy.
Two of the predominant types of relationships in knowledge-representation systems are predication and the universally quantified conditional. Predication relationships express the notion that an individual entity is an example of a certain type (for example, "John is a bachelor"), while universally quantified conditionals express the notion that a type is a subtype of another type (for example, "A dog is a mammal", which means the same as "All dogs are mammals").
Taxonomies are often represented as "is-a" hierarchies where each level is more specific (in mathematical language "a subset of") the level above it. For example, a basic biology taxonomy would have concepts such as "mammal", which is a subset of "animal", and "dogs" and "cats", which are subsets of "mammal". This kind of taxonomy is called an is-a model because the specific objects are considered as instances of a concept. For example, "Fido" is-an instance of the concept "dog" and "Fluffy" is-a "cat".<br>
In linguistics, is-a relations are called hyponymy. Words that describe categories are called hypernyms and words that are examples of categories are hyponyms. In the simple biology example, "dog" is a hypernym and "Fido" is one of its hyponyms. A word can be both a hyponym and a hypernym. For example, "dog" is a hyponym of "mammal" and also a hypernym of "Fido".
Research.
Researchers reported that large populations consistently develop highly similar category systems. This may be relevant to lexical aspects of large communication networks and cultures such as folksonomies and language or human communication, and sense-making in general.