A hierarchy is system of ranking and organizing things. Different fields use the word in slightly different ways, but a particular definition, which the article will attempt first, captures the core of almost all uses. Originally, "hierarchy" was a word meaning "rule by priests". Since hierarchical churches such as the Roman Catholic and Eastern Orthodox churches had tables of organization that were "hierarchical" in the modern sense of the word, the term came to refer to more general organizational methods.
A precise, mathematical definition of hierarchy will be given in the next section. This section will try to explore the ideas behind that more compact definition.
A hierarchy is based on an asymmetrical relationship, such as "is the boss of", "is part of", or "is better than". Such relationships are "asymmetrical" in the sense that if they "work one way", they don't "work the other". For example, if Sally is the boss of Jim, then Jim is not the boss of Sally. When two nodes are related, one is designated the "superior" (or sometimes the "parent") and the other the "subordinate" (or sometimes the "child"). In the intuitive case of the "is the boss of" relation, the boss is the superior and the employee is the subordinate.
A hierarchy's asymmetrical relationship can link entities in one of three ways: directly, indirectly, or not at all. The illustration shows a direct link between the craft and culture sections; the craft section is directly linked to the culture section by the "contains" relationship. This is akin to how your boss in directly in charge of you. In contrast, the illustration shows an indirect link between craft and encyclopedia; the craft section is only "contained" by the encyclopedia as a whole by virtue of being "contained" by the culture section. This is akin to how the CEO of a company is in charge of a factory worker only via middle management. Finally, there is effectively no link between the art and the craft sections; neither section contains the other. This is akin to two co-workers, neither of whom is the other's boss.
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Every member is reachable from any other by following the relationship in either direction, but there is no way of coming back to a particular member by always following the relationship in the same direction.
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A hierarchy can thus be represented as a connected directed acyclic graph.
Many aspects of the world are analyzed, arguably fruitfully, from a hierarchical perspective. Science provides the following examples:
Many human organizations, such as businesses, churches, armies and political movements are structured hierarchically, at least officially; commonly superiors, called bosses, have more power than their subordinates. Thus the asymmetrical relationship might be "has power over". (Some analysists question whether power "really" works as the traditional organizational chart indicates, however.)
Feminists talk about a hierarchy of gender, in which a culture sees males or masculine traits as superior to females or feminine traits. In the terms above, these feminists present us a hierarchy of only two nodes, "masculine" and "feminine", connected by the asymmetrical relationship "is valued more highly by society". An example of this usage:
Hierarchy is often used to control complexity in engineering endeavors. In object-oriented programming, for example, classes are organized hierarchically; the relationship between two related classes is called inheritance.
The pitches and form of Tonal music are organized hierarchically, all pitches deriving their importance from their relationship to a tonic key, and secondary, "feminine", themes in other keys are brought back to the tonic in a recapitulation of the primary, "masculine", theme. Susan McClary connects this specifically in the sonata-allegro form to the feminist hierarchy of gender (see above) in her book Feminine Endings.
The Wikipedia community is remarkable for being not overtly hierarchically structured, as no contributor possesses inherently higher standing than another. However, some would note that although there is no explicit hierarchy there are social norms which make contributions unequal. Some contributors have more influence because their edits command higher respect and administrative privileges.
Those who frequent Wikis might label Wikipedia's organization "wikiarchical".
The concept of hierarchy qualifies as interdisciplinary.
From the greek hieros, sacred + archos, ruler.
Principles and annotated bibliography of hierarchy theory
Generalizations: Structure
Specializations:
General considerations (informal)
General considerations (formal)
Examples of reasoning with hierarchies
In all of these examples, the asymmetric relationship is "is composed of".Social hierarchies
Note that when feminists and other social critics use the word hierarchy, they usually hope to evoke negative connotations; hierarchy, for them, is a bad thing. In these contexts, hierarchy and power structure are basically synonyms.Hierarchical nomenclatures in the arts and sciences
Misc
History of the word
External link
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Relevant examples: