A generalization relationship (sometimes called an is-a relationship) indicates that a specialized (child) model element is based on a general (parent) model element. The parent model element can have one or more children, and any child model element can have one or more parents. It is more common to have a single parent and multiple children. To comply with UML semantics, the related model elements must be the same type; a generalization relationship can be created from actor to actor or from use case to use case; however, it cannot be created from actor to use case.