"Whatever we learn has a purpose and whatever we do affects everything and everyone else, if even in the tiniest way. Why, when a housefly flaps his wings, a breeze goes round the world; when a speck of dust falls to the ground, the entire planet weighs a little more; and when you stamp your foot, the earth moves slightly off its course... And it's much the same thing with knowledge, for whenever you learn something new, the whole world becomes that much richer."
In the previous chapter, you learned about the information model of the Semantic Web: the Resource Description Framework, or RDF. RDF provides a virtually limitless model for describing information. You can say anything you want about anything you want. The drawback of all the flexibility and expressiveness of RDF is that used alone, it lacks explicit support for specifying the meaning, or semantics, behind the descriptions.
Fortunately, the original vision for the Semantic Web considered the fact that developers and users need some way of specifying rich semantic descriptions of concepts and relationships to exchange information effectively. RDF Schema (RDFS) and the OWL Web Ontology Language provide these capabilities.
The purpose of this chapter is to provide you with the knowledge necessary to add semantics to your web of RDF data. Semantics are the key to incorporating domain knowledge into RDF data, making the descriptions richer and more meaningful. ...