Defining Properties

Properties are created at a global level and then related to different classes. In our ontology, we require two properties:

•

hasEdition to carry information about the edition of a product. The edition can be Enterprise, Professional, or Home. We will create this property as an object property. Doing this enables us to relate one resource to another. In this case we wish to relate instances of the XMLSpy class to instances of the Edition class via the hasEdition property. The class (or classes) that the property applies to is called the property's domain, while the set of values the property can take is called the property's range.

•	version, which is a literal value indicating the year in which a product is released. We will create this property as a datatype property. It relates instances of the XMLSpy class to a positive integer (which is the year of release and gives the version of the product).

Properties are created in the same way that classes are created, by clicking the Add New button and then specifying the name of the property to be created. To create a property, do the following:

2.	This creates a line for the newly created object property. In this line, enter prod:hasEdition as the name of the new object property.

3.	Now add a datatype property by: (i) clicking the Add New button and selecting owl:DatatypeProperty, and (ii) entering prod:version as the name of the datatype property.

You have now created two properties: (i) an object property called hasEdition, and (ii) a datatype property called version. The Properties tab should now look like this:

The first thing you should note when working with OWL properties in SemanticWorks is that object properties and datatype properties are indicated with slightly different symbols in Detail View. Double-click the Detail View icon

to see the Detail View symbol for each property:

Object properties are indicated with an O icon in the top-left corner, datatype properties are indicated with a DT icon. The icons to the right of these two icons are actually toggle switches for specifying the cardinality constraints and characteristics of properties. They are toggles for, from left to right, setting the property to be a functional property; an inverse-functional property; a transitive property; and a symmetric property. Note that a datatype property is only allowed the functional property relationship.

You will now define the relationships and characteristics of the two properties you have created. Do this as follows:

1.	Double-click the Detail View icon of the hasEdition property. This brings up the Detail View of the property.

2.	Right-click the prod:hasEdition box, and, from the context menu that appears, select Add Domain (screenshot below).

4.	Click the down arrow in the Class box, to drop down a list of available classes, and select prod:XMLSpy (screenshot below).

The class prod:XMLSpy is set as the domain of the property prod:hasEdition. This relationship states that the hasEdition property is applicable to the class XMLSpy.

In the same way that you set the domain of the property, now set the range of the property: (i) right-click the hasEdition property box; (ii) select Add Range; (iii) right-click the Range connector box; (iv) select Add Class; (v) from the dropdown list in the Class box, select the class prod:Edition. The Detail View of the hasEdition property should look like this:

We wish to specify that the property hasEdition can take only one instance of the Edition class as its value. This is done by specifying that the hasEdition property is functional. To make the property functional, click the f icon (functional property icon) in the hasEdition property box. The Detail View of the hasEdition property should look like this:

Notice that the f icon in the hasEdition property box is highlighted, indicating it is toggled on.

For the datatype property prod:version, you will define a domain similarly as defined above for the object property has:Edition. Set the domain to the class XMLSpy. For the range, we wish to define the XML Schema datatype xsd:positiveInteger. Do this as follows:

The version property is now a functional property. It is applicable to instance of the class XMLSpy (its domain) and can take values that are of the XML Schema datatype xsd:positiveInteger (its range). The Detail View of the version property should look like this:

When you switch to the Properties Overview (that is, the Properties tab in the Ontology Overview), notice that the domains of the selected property are displayed in the subsidiary window (screenshot below).

Click the Detail View button of a domain class to go directly to the Detail View of that class.

You can see the properties of a selected class in the subsidiary Class Properties window of the Classes Overview (Classes tab in the Ontology Overview). See screenshot below.

Click the Detail View button of a property to go directly to the Detail View of that property.

At this stage, check the syntax (RDF/OWL | Syntax Check) and the semantics (RDF/OWL | Semantics Check) of your ontology, making sure that the OWL Lite level is selected. Your OWL Lite ontology till this point should be both well-formed and at least partially consistent.

Both properties (hasEdition and version) were set to have the class XMLSpy as its domain, meaning that both properties are applicable to the XMLSpy class. Now check the effect of these definitions on the XMLSpy class. Do this as follows:

3.	Go to the Detail View of the class XMLSpy (by clicking the Detail View icon next to the class entry). The Detail View of the XMLSpy class should look something like this:

Here we see that the class XMLSpy is a subclass of the class Product, and has two properties: the object property hasEdition and the datatype property version.