What is the UMLS?

The UMLS, or Unified Medical Language System, can be described as a large archive made up of different biomedical terminologies. The archive was originally created in the year 1986, and since its creation, it has served a storehouse for all of the different vocabularies considered relevant to biomedical practices.

History and Purpose of the Unified Medical Language System

In 1986, Director of the Library of Medicine Donald A.B. Lindberg M.D. spearheaded the UMLS project. Since its inception, its purpose has been to ensure that biomedical facilities have an appropriate degree of access to resources meant to process natural language.

To date, the UMLS has been consistently managed by its designer, the US National Library of Medicine. The UMLS has been consistently refreshed for new information on a quarterly basis.

The system was developed as a way to account for the serious challenge presented to researchers overwhelmed by the large volume of resources available for reference. Ideally, UMLS can assist researches by offering them an easier avenue of access to the relevant literature.

With easy access to the right literature, researchers have the ability to further develop computer systems that can more effectively process and understand biomedical language vocabulary.

There are two significant obstacles that the UMLS helps to surpass: the difficultly of distributing information to all of the relevant parties who make up segmented databases, and the different expressions of similar concepts within uniquely-designed machine sources and professionals.

Sources of Knowledge and Licensing

Any users of the UMLS must adhere to two different requirements in order to receive licensing: a signature of the UMLS agreement, and annual reports on usage. If the user happens to be involved in academia, then the UMLS may be used for research purposes. In the event that the user isn’t using the system for an explicitly academic purpose, it may be used for either production or commercial purposes with the acquisition of copyright licenses.

The foundation of the UMLS is the Metathesaurus. Within the Metathesaurus are several million different concepts and their associated concept names. External resources, such as the databases for gene sequences, can be linked from with the Metathesaurus’s storehouse of concepts. No matter what external resources are linked, the hierarchical information from each of the different source vocabularies is contained and organized within.

For each of the concepts within the UMLS, there is an associated semantic type; these form what is collectively referred to as the Semantic Network. Every single one of the semantic types within the Semantic Network is associated with a range of informational identifiers, examples, definitions, and its associated relationships as well. All in all, there are 135 different semantic types, and this network of semantic types collectively contains 54 different relationships.


In a sense, the Unified Medical Language System can be compared to an ontological thesaurus. Every essential concept in the biological medicine field is made readily available to those who are professionally involved in medical informatic development. The compendium is available to be used at no cost.

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