Extending Existing Ontologies For Your Use

There are many ontologies that have already been created and may be of use in your projects. However, the likelihood of a single, pre-existing ontology that meets all of your requirements may be small. This doesn't mean that you need to start from scratch to create an ontology that satisfies your needs. As an alternative, you can build upon existing ontologies by extending them using standard OWL methods, as demonstrated below.


Namespaces are a feature of XML that were created to provide modularity and allow the re-use of XML code between projects. These same benefits apply to OWL, a type of XML, and namespaces can be declared in your ontology.

When you want to refer to concepts or resources contained within an existing ontology without importing a full version of the external ontology, then you can simply invoke the ontology's namespace, which you can declare in your own ontology. Below is an example of declaring a namespace and then using it in an OWL ontology.

Example Namespace Statement

<rdf:rdf xmlns:owl="<a href="http://www.w3.org/2002/07/owl#">">http://www.w3.org/2002/07/owl#"></a> </rdf:rdf> 

This creates the namespace of 'owl', which acts as both a unique identifier and shortcut for the OWL ontology.

Example Namespace Usage

<owl:ontology><rdfs:comment>An example ontology that uses OWL</rdfs:comment></owl:ontology>

Here, the namespace owl that we created above is used with the concept ontology, which is defined in the OWL standard. This is the section where the ontology itself is described using metadata.


When creating your own ontology, you may directly import the entirety of a second ontology to be contained within the first. This takes the entire external ontology, including all of its imports and namespaces, and includes them in your ontology in a very literal sense, almost as if you had copied and pasted the text from one file to another.

However, the resources from the external ontology will not actually appear in your OWL file as they do in their original file. All you will see is the import statement, which looks like the following:

<owl:imports rdf:resource="<a href="http://mmisw.org/ont/cf/20081116T050933/parameter">">http://mmisw.org/ont/cf/20081116T050933/parameter"></a> </owl:imports> 

The import statements are read by inferencing engines, RDF stores, and programs like Protege. Once your ontology file is processed via one of the tools, all of the imported ontologies become available for use in queries and inferencing.

Suggested Citation

Alexander, P. 2011. "Extending Existing Ontologies For Your Use." In The MMI Guides: Navigating the World of Marine Metadata. http://marinemetadata.org/guides/vocabs/ont/existing/extending. Accessed September 26, 2020.