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next section. Which option you choose for your ontology will depend on the specific requirements you 
have as well as the standards established by your organization or organizations that you work with.  
Finally, another name related concept you should be aware of is the concept of a namespace. If you have 
worked with most modern programming languages such as Python or Java, you are already familiar with 
the concept of a namespace. The concept is identical in OWL. A namespace is used to avoid naming 
conflicts between different ontologies. For example, you may have a class called Network in an ontology 
about telecommunications. You might also have a class called Network in an ontology about graph 
theory. The two concepts are related but are different. Just as with programming languages you use 
namespace prefixes to determine what specific namespace a name refers to. E.g., in this example you 
might have the prefix tc for the Telecom ontology and gt for the Graph Theory ontology. Thus, when 
you referred to the Network class for the Telecom ontology you would use tc:Network and 
gt:Network for the graph theory class.  
Note that you already have some experience with other namespaces. The OWL namespace prefix is owl 
and is used to refer to classes such as owl:Thing and owl:Nothing. The Resource Description 
Framework Schema (RDFS) is a model that OWL is built on top of and thus some properties that 
ontologies use such as rdfs:label leverage this namespace.  
In the bottom view of the Active ontology tab there is a tab called Ontology Prefixes. This tab shows all 
the current namespace mappings in your ontology. There are certain concepts from OWL, RDF, RDFS, 
XML and XSD that are required for every ontology, so those namespaces are by default mapped in every 
new Protégé ontology. There is also a mapping to the empty string for whatever the namespace is for your 
ontology. This allows you to display and refer to entities in your ontology without entering a namespace 
prefix. If you look at that tab now you should see a row where the first column is blank, and the second 
column has the base IRI for your ontology. It should be the same IRI as the Ontology IRI at the top of the 
Active ontology tab, except it also has a # sign at the end. E.g., the Pizza tutorial developed for this 
tutorial has an IRI of: http://www.semanticweb.org/pizzatutorial/ontologies/2020/PizzaTutorial and the 
row that has a blank first column in Ontology Prefixes has the IRI: 
http://www.semanticweb.org/pizzatutorial/ontologies/2020/PizzaTutorial#.