Semantic Web Programming

Chapter 5. Modeling Knowledge in the Real World

"Welcome to the real world"

—Morpheus, The Matrix

Most of the discussion so far about RDF, OWL, and ontologies has been very abstract. To this point, you've learned what they are, but not as much about how to use them in practical applications and how to utilize the information they enable you to model.

This chapter is about using OWL ontologies in the real world. In it, you learn about:

• How ontologies fit into practical applications

• The concept of inference and how it is critical to the implementation of the semantics of OWL

• Profiles of OWL, their purposes, and how they can be used to provide desirable computational characteristics to systems using OWL

• Critical design principles for information-management applications

Exploring the Components of the Semantic Web

OWL ontologies allow you to describe things using explicit semantics. In Chapter 4, we often said that the semantics of various OWL constructs imply other information. For example, a statement asserting that two classes are related using rdfs:subClassOf implies that all members of the subclass are also members of the superclass. Returning to the example in Chapter 4, Daisy is a member of the class ex:Canine because it is explicitly stated in the following RDF excerpt:

@prefix ex: <http://example.org/>. ex:Mammal rdf:type owl:Class. # Canine is a subclass of Mammal ex:Canine rdf:type owl:Class; rdfs:subClassOf ex:Mammal. # Daisy is implicitly a member of the class Mammal ex:Daisy rdf:type ...