Knowledge Representation by Networks
Taxonomic Knowledge
Vital part of knowledge representation is the organization of objects into categories.
Uses of Categories
Much reasoning takes places at the level of categories, even through interaction with the world takes place at the level of individual objects.
Example: A shopper might have the goal of buying a basketball; rather than a particular basketball such as BB9.
Categories also serve to make predictions about objects once they are classified. By concluding the presence of certain objects from perceptual input, category membership can be concluded the perceived properties of the objects and then uses category information to make predictions about the objects.
Example: From its green, mottled skin, large size, and ovoid shape, it can be concluded that an object is a watermelon, from this, it can be concluded that it would be useful for fruit salad.
Subclass relations organize categorizes into a taxonomy or taxonomic hierarchy.
Example: Systematic biology aims to provide a taxonomy of all living and extinct species. Taxonomies are also an important aspect of general commonsense knowledge.
First-order logic makes it easy to state facts about categories, either by relating objects to categories or by quantifying over their member,
An object is a member of a category.
Example: BBg ∊ Basketballs.
A category is a subclass of another category.
Example: Basketballs ⊂ Balls.
All members of a category have some property.
Example: x ∊ Basketballs ⇒ Round(x).
Members of a category can be recognized by some properties.
Example: Orange(X) Λ Round(x) Λ Diameter(x),:= 9.5" Λ x ∊ Balls ⇒ x ∊ Basketballs.
A category as a whole has some property.
Example: Dogs ∊ DemesticatedSpecies.
One can even have categories of categories of categories, but they are not much use.
Although subclass and member relations are the most important ones for categories, it is necessary to state relations between categories that are not subclasses of each other.
Example: If it is said that Males and Females are subclasses of Animals, then it is not said that a male cannot be a female.
