6.1 Type hierarchies
Types can be organized in type hierarchies. Type hierarchies are networks of types (called 'lattices') where the types are ordered by a partial order. This partial order is called the "subtype relation", and is symbolized by "≤". For example, "A ≤ B" means that the type A is a subtype of the type B. For example, "Bird ≤ Animal" means "Bird is a subtype of Animal".
Example in graphical form
An example of a type hierarchy could be as follows:
"Example of type-hierarchy"
The lattice-notation is to be read as follows:
Example in linear form (Prolog+CG form)
As already noted, in Module II of this course, we will be studying a system called Prolog+CG. This system has a mechanism for specifying a type hierarchy in linear form. The above could be written as follows in Prolog+CG:
Entity > Living, NonLiving. Living > Person, Animal. Person > god, HumanBeing. Animal > Bird, Fish, Mammal. Mammal > Elephant.
Prev: 6 Core ontological ideas
Up: 6 Core ontological ideas
Next: 6.2 Subtype relation