Taxonomy (Multi-Level Vocabulary)

Definition, description and example of a taxonomy

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Definition of Taxonomy

A multilevel controlled vocabulary in which metadata values are grouped according to subject-specific classes, usually hierarchical.


Taxonomies are an organizational structure in which metadata values are grouped according to subject-specific classes. Each class has a specific description, which is the set of characteristics that each member of a class exhibits. Taxonomies begin with the broadest of classes, and continue to narrow until the final class is reached.

The classes that are included in a taxonomy will depend largely upon the discipline of the metadata values. So, while a geological taxonomy might include classes like metamorphic, igneous and sedimentary, a chemical taxonomy might include classes like solid, liquid and gas.

These classes provide characteristics for each of the members of a class. The taxonomy is used to describe a particular thing, and usually culminates in a unique identifier for each member.

Note: While taxonomies tend to include subject-specific, narrow classes, another type of classification, subject headings, tends to include broader classes.


Perhaps the most well-known taxonomy is the Linnaean taxonomy, which uniquely classifies living things. In its simplest form, the Linnaean taxonomy has seven main levels. As an example, consider the Linnaean classification for humans:

  • Kingdom: Animalia

    Characteristic: eukaryotic cells with a cell membrane but no cell wall, multi-cellular, heterotrophic

  • Phylum: Chordata

    Characteristic: notochord, dorsal nerve cord, and pharyngeal gill slits

  • Class: Mammalia

    Characteristic: endothermic, hair and mammary glands (which are used to nourish the young)

  • Order: Primates

    Characteristic: collar bone, eyes facing forward, grasping hands with fingers, two types of teeth

  • Family: Hominidae

    Characteristic: upright posture, large brain, stereoscopic vision, flat face, hands and feet with different functions

  • Genus: Homo

    Characteristic: s-curved spine

  • Species: sapiens

    Characteristic: high forehead, well-developed chin, skull bones thin

Notice, as human beings, we are given a unique identifier (Homo sapiens), and we exhibit all the characteristics listed (in other words, since our classification is at the bottom of a nested list, we can inherit all the characteristics of the "super-classes"). To completely classify humans in this taxonomy, we need to use the term Homo sapiens, but you could also call human beings primates. This would not be the narrowest classification, but it is an accurate classification.

Suggested Citation

Neiswender, C. 2011. "Taxonomy (Multi-Level Vocabulary)." In The MMI Guides: Navigating the World of Marine Metadata. Accessed December 7, 2019.