To find out more watch the Semantic standards training

Introduction to the standard

The Unified Code for Units of Measure (UCUM, https://ucum.org/trac) is a compositional code system intended to include all units of measures being contemporarily used in international science, engineering, and business. UCUM units can be composed by using the UCUM expression syntax. UCUM, similarly to LOINC, is released and maintained by the Regenstrief Institute. It is adopted by standard organization such as DICOM (https://www.dicomstandard.org/) or HL7 (https://www.hl7.org/) and is strongly encouraged by LOINC (https://loinc.org/). UCUM is used as one recommended standard for the SPHN concept Unit (https://biomedit.ch/rdf/sphn-ontology/sphn/unit).

Technical specification

Next to standard units such as L=liters, g=grams, UCUM allows for:

  • Prefixes e.g. k for ‘kilo’ or u for ‘micro’

  • Annotations in {} e.g. mU/g {Hgb} for ‘miliUnits per gram Hemoglobin’

  • Scaling factors such as 10*X e.g. 10*3/ul for ‘thousand per microliter’

  • Lexical elements in [] e.g. mm[Hg] for ‘millimeters of mercury’

  • Operators e.g. . for ‘multiplications’ and / for ‘division’

Conventions in use in SPHN

The UCUM clearly defines each available unit with concise semantics, but also allows for the use of free-text annotations that can be added to defined variables or used instead of a unit.

Although this practice is discouraged, it is widely used in several scientific fields, such as clinical research. To address this issue, SPHN has developed a series of recommendations for the use of UCUM annotations when deemed necessary:

  • Use of the English language

  • Avoid abbreviations

  • Use of the singular form

  • Use of lower-case spelling

Example: The French term ‘Spécimen’, often used as part of units such as ‘µg/Spécimen’ would become ug/{specimen}

Implementation in RDF for SPHN

For the SPHN RDF file, we did not implement full support for the syntax. We rely on a large library of pre-built valid UCUM codes from the National Library of Medicine, National Institutes of Health, U.S. Department of Health and Human Services with content contributions from Intermountain Healthcare and the Regenstrief Institute (download list, and additional information, Version 1.5, Released 06/2020.).

In addition, a couple of units from the SPHN dataset (e.g. cGy, MBq, mCi), not included in this library, has been added.

The namespace used in the RDF to refer to the UCUM terms is: <http://biomedit.ch/sphn-resource/ucum/>.

Since UCUM does not have a release cycle, the versioning relies on the year when the RDF is generated. The version IRI is provided for each version of UCUM in RDF (e.g., https://biomedit.ch/rdf/sphn-resource/ucum/2021/1/), which is composed of the namespace followed by the year the RDF is being generated and the version of the RDF generated for that year.

In this RDF, a root class is generated (https://biomedit.ch/rdf/sphn-resource/ucum/UCUM). The UCUM codes are provided as owl:NamedIndividuals, with a rdfs:label, a rdfs:comment and are linked to the ucum:UCUM root class (see example below of the unit kilogram):

ucum:kg a owl:NamedIndividual,
      ucum:UCUM ;
  rdfs:label "kg" ;
  rdfs:comment "kilogram" .

All individuals are directly usable in any project as instance data.

This release contains a flat list of the UCUM terms in RDF. There hasn’t been any hierarchy established to cluster the terms under different classes.

If you need an UCUM code not present in the list, please submit a request to the DCC dcc@sib.swiss, we will then include it in the next SPHN UCUM RDF release.

Availability and usage rights

The RDF file is available via the Terminology Service.

The copyright follows the instructions provided by Regenstrief Institute. UCUM is Copyright © 1999-2013 Regenstrief Institute, Inc. and The UCUM Organization, Indianapolis, IN. All rights reserved. See TermsOfUse.