Resource Description Framework
This system of defining everything with URIs, and using this to describe the relationships between things, has been formalized in a system known as the Resource Description Framework (RDF). In this section, we’ll look at enough RDF to give you a head start on the rest of the book. For a much deeper insight into RDF, take a look at Practical RDF (O’Reilly).
Because RDF is quite abstract—its ability to be written in different ways notwithstanding—in this chapter, we are going to look at what the RDF developers call the “data model,” which we can call “the really simple version, in pictures.”
Resources, PropertyTypes, and Properties
As before, within the data model, anything (an object, a person, a document, a concept, a section of a document, etc.) can have a URI. In RDF anything addressable with a URI is called a resource .
Some resources can be used as properties of other resources. For example, the concept of “Author” has a URI of its own (all concepts can), and other resources can have a property of “author.” Such resources are called PropertyTypes .
A property is the combination of a resource, a PropertyType, and a value. For example, “The Author of RSS and Atom is Ben Hammersley.” The value can be a string (“Ben Hammersley” in the previous example), or it can be another resource—for example, “Ben Hammersley (resource) has a home page (PropertyType) at http://www.benhammersley.com (resource).”
Nodes and Arcs
RDF’s data model is most easily understood ...