Now we'll define a Class with some attributes. The next few lines describe a domain-specific range restriction. To whit, the parent of a Person is also a Person. The syntax used here is a cliche, i.e., it is almost always used as shown, except for the name of the resource in the OnProperty element, which will give the name of the Property to be restricted, and the resource associated with the toClass element, which will give the name of the Class to which the Property is restricted. That's the end of the Person class.
Mother is defined similarly but using a variant notation.
A UniqueProperty is one with cardinality 1, so we can omit that sub-element from Mother's definition. See also UnambiguousProperty, a property whose object uniquely identifies its subject. Sometimes, we like to refer to mothers using the synonym mom. If x's parent is y, then y is x's child. This is defined using the inverseOf tag.