The DwC operational unit is primarily based on taxa, their occurrence in nature as documented by observations, specimens, and samples, and related information.
Though the data types and constraints are not provided in the term definitions, recommendations are made about how to restrict the values where appropriate, for instance by suggesting the use of controlled vocabularies.
DwC standards are versioned and are constantly evolving, and working groups frequently add to the documentation practical examples that discuss, refine, and expand the normative definitions of each term.
Darwin Core was originally created as a Z39.50 profile by the Z39.50 Biology Implementers Group (ZBIG), supported by funding from a USA National Science Foundation award.
A TDWG task group was created to revise the Darwin Core, and a ratified metadata standard was officially released on 9 October 2009.