OWL Classes

Generally speaking, OWL classes can be considered as sets of individuals that share similar characteristics. These classes are organized in hierarchies, of which owl:Thing is the root class. Every individual in the ontology is a member of the class owl:Thing. Thus, each class you create is implicitly a subclass of owl:Thing. A class may be a subclass of more than one parent class. Likewise, an individual may belong to more than one class.

OWL classes are described through so-called class descriptions. A class description describes an OWL class, either by a class name or by specifying the complex class expression, representing an unnamed anonymous class. OWL distinguishes six types of class descriptions:

These class descriptions are distributed over the following tabs in the Entity Properties panel:

For instructions on how to create a class, see Create a Class.

Online References

Further information is available at the following Web sites:

Class Restrictions

OWL can be used to model situations in which the members of a particular class must have certain properties. You can use various restriction statements to indicate that something should apply to all values of a property versus only for some members. In addition, you can even specify a particular value for a property of all members of a class.

OWL distinguishes two kinds of restrictions: value restrictions and cardinality restrictions. A value restriction puts constraints on the range of the property when applied to this particular class. A cardinality restrictions puts constraints on the number of values the property can take, in the context of this particular class.

OWL provides the following value restrictions:

In addition, OWL provides the following cardinality restrictions:

OWL Classes - Class Restrictions

Class restrictions can either be specified as Super Restrictions or Equivalent Restrictions. If you add the class restriction in the Super Restriction section, the class under consideration will become a subclass of the restriction class (i.e. you define a necessary condition for the class). On the other hand, if you add the class restriction in the Equivalent Restrictions section, both, the restriction class and the restricted class, will be interpreted as equivalent, which means that they always have exactly the same members (i.e. you define a necessary and sufficient condition for the class).

For instructions on how to create a class, see Create a Class. To create a class restriction, proceed as follows.

  1. Select a class in the Ontology Navigator.
    The class will be displayed in the Entity Properties panel.
  2. Enter a property.
    Enter the property used to restrict the class. You can also use the auto-complete feature of the OWL Perpective.
  3. Select a quantifier.
    Select the appropriate value constraint or cardinality constraint.
  4. (Optional) Select a number.
    This only applies if you have selected a cardinality constraint.
  5. Select a range.
    Select the class for which the property under consideration only should have values.
  6. Click Add.
    The class restriction will be created. To discard your changes, click Cancel.

Note – The ranges of restrictions can be entered using the Manchester OWL Syntax. For more information, see Manchester Syntax.
Taxonomy

On this tab you can define classes through class axioms. The simplest form of a class axiom is a class description of type 1 above. It just states the existence of a class, using owl:Class with a class identifier. Class axioms typically contain additional components that state necessary and/or sufficient characteristics of a class. OWL contains three language constructs for combining class descriptions into class axioms:

In addition to these language constructs, the OWL Perpective allows you to specify the super classes of a class, which is the same as making the class under consideration a subclass of another (parent) class. For example, you will notice that owl:Thing is the super class of all other classes because every user-defined class is implicitly a subclass of owl:Thing.

OWL Classes - Taxonomy

To create a class axiom, proceed as follows:

  1. Select a class in the Ontology Navigator.
    The class will be displayed in the Entity Properties panel.
  2. Go to the Taxonomy tab.
    The class axioms will be displayed.
  3. Create a class axiom.
    In the Create New text box, enter a class name. You can also use the auto-complete feature of the OWL Perpective. In addition to simple classes you can also enter complex class descriptions using the Manchester Syntax.
  4. Click Add.
    The class axiom will be created. To discard your changes, click Cancel.
To display restriction in the Class Taxonomy tab, you can change the settings in the Preferences(main NeOn Toolkit preference site - General)
Than it looks like this:

OWL Classes - Taxonomy (including restrictions)

Annotations

Usually, annotations are used to add information to resources of the ontology. They contain useful information such as who is the creator or what are the readable labels and comments for single elements of the ontology.

For information on how to create an annotation, see Create an Annotation.

OWL Classes - Annotations