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4.6 OWL Properties  
OWL Properties represent relationships. There are three types of properties, Object properties, Data 
properties and Annotation properties. Object properties are relationships between two individuals. Data 
properties are relations between an individual and a datatype such as xsd:string or xsd:dateTime. 
Annotation properties also usually have datatypes as values although they can have objects. An 
annotation property is usually meta-data such as a comment or a label. In OWL only individuals can have 
values for object and data properties, but any entity can have an annotation property value since meta-data 
applies to all entities. Annotation properties usually can’t be reasoned about. For example, SWRL rules 
which we will cover later cannot view or change the value of annotation properties. In this chapter we 
will focus on Object properties. Data properties are described in Chapter 5. In the current version of the 
tutorial we are only discussing the annotation property rdfs:label (see chapter 7) however they are 
fairly intuitive.  
Properties may be created using the Object Properties sub-tab of the Entities tab shown in figure 4.11. 
Just as all OWL classes ultimately are a subclass of owl:Thing, all properties are ultimately a sub-
property of owl:topObjectProperty. A sub-property is similar to a subclass except it is about the 
tuples in a property. For example, hasFather would be a sub-property of hasParent because all the 
tuples in hasFather are in hasParent but not vice versa. E.g., if Sasha hasFather Barack then she 
also hasParent Barack. However, she also hasParent Michelle but it is not the case that she 
hasFather Michelle. Rather she hasMother Michelle, i.e., hasMother is also a sub-property of 
hasParent.  
The GUI for entering properties is also similar to that for entering classes. The first icon with one box 
under another creates a sub-property of the selected property. The second icon showing two boxes at the 
same level creates a sibling property to the selected property and the icon with an X through a box deletes 
the selected property.  
Exercise 9: Create some properties 
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1. Select the Object properties sub-tab of the Entities tab (see figure 4.11). 
2. Make sure owl:topObjectProperty is selected.  Click on the nested box icon at the left to create a 
new sub-property of owl:topObjectProperty.  When prompted for the name of the new property 
type in hasIngredient.  
3. Just as you can use a wizard to create multiple classes you can also use one to create multiple 
properties. Select hasIngredient and then select Tools>Create object property hierarchy. Enter the new 
property names hasTopping and hasBase. Select Continue and accept the default that the object properties 
are not disjoint.  
4. Synchronize the reasoner. Your window should now look like figure 4.11.  
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For those familiar with the Entity-Relationship model, OWL object properties are similar to 
relations and data properties are similar to attributes.  Object properties are similar to 
properties with a range of some class in OOP and data properties are similar to OOP properties 
with a range that is a datatype.