Inheritance mechanism of type-level attributes

As already said, a new type definition could override the values of some of the attributes of the supertype. The new values, though, might still bear some relation with the ones in the supertype. This has led to the definition of a few different inherintance semantics. The inher field specify how the new value of the declared attribute relates to the one in the supertype. It can assume one of the following values (see 1.5 also):

• redef: The attribute value is completely redefined.
• append: The new value must appended at the end of the one specified in the supertype. Such an usage is meaningful only for the Bool and Pred domains.
• inner: The new value is inserted in a corresponding ``placeholder'' (keyword inner) purposedly declared in the supertype. It can be used only if the value is a Prolog predicate ( Pred).

  
Figure 1.5: Inheritance mechanism.