New simple types can be derived by restriction. If a complex type is a restriction of another type we can derive a subclass relationship between them. Restrictions are easier to translate into OWL than extensions because they only add new constraints, thereby reducing the set of valid instances. The occurrences of elements and attributes may be reduced (though not below the minimum of the parent class) and their types may be narrowed. A restriction defines a subset of instances of its base type. OWL may be used to declare restrictions of simple types but is not able to define constraints on the new value space other than by enumeration.

• Restriction of Complex Content

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