Citing Terms

Ontologies and terms within ontologies use addresses so they can be located. To do this, ontologies and their terms are assigned URIs, making them identifiable and useable by people and software.

Where Do URIs Come From?

Unfortunately, there is no one right answer for how URIs are assigned to resources. There are several factors that influence how providers choose to assign URIs to their ontologies:

  • Where will the ontology reside? Is it hosted on a Web server, submitted to a registry, or using another method of making it available online? Ontologies submitted to a registry may have a URI assigned by the registry itself, whereas an ontology hosted on a Web server is just like any other file, meaning it resides in a folder hierarchy wherever the provider chose to include it on the server.
  • Does the URI include the version identifier for the ontology? As groups make modifications to an ontology, they are versioned to make apparent changes in definitions or structure. Knowing whether or not a version is included in the URI can help you when trying to decide which URI to use for a resource.
  • Does the URI help people understand what the resource is? There is some disagreement about this point, and not all ontology providers believe it is important to have URIs that have meaning. However, MMI recommends that semantics be included when assigning URIs as it may provide a way for people to understand a resource simply based on the URI string.

MMI Recommendations

MMI has developed a set of recommendations for ontology providers that are currently in use on the MMI Registry and Repository. The full recommendation is available but is beyond the scope of this document. What follows is a basic description of the URI construction that MMI recommends and uses in its Ontology Registry and Repository.

MMI recommends that URIs are constructed as follows:

URLs for Ontologies

http://{hostDomain}/{ontologiesRoot}/{authority}/{version}/{resourceType}.owl Example: http://mmisw.org/ont/mmi/20081116T071659/sensor

URLs for Concepts (Terms)

http://{hostDomain}/{ontologiesRoot}/{authority}/{version}/{resourceType}/{shortName} Example: http://mmisw.org/ont/mmi/20081116T071659/sensor/ProcessOutput

URIs require no inherent semantics in their construction, meaning that http://aabbcc112233.org is just as valid as http://ontologiesforscience.org. The second representation has much more meaning for a human, though a machine doesn't care either way. MMI recommends that URIs should actually be formulated to have meaning so that a human reading the URI will recognize what it represents and, potentially, what to do with it.

Suggested Citation

Alexander, P. 2011. "Citing Terms." In The MMI Guides: Navigating the World of Marine Metadata. http://marinemetadata.org/guides/vocabs/ont/existing/citing. Accessed December 14, 2019.