So where does this all leave us? How do we infuse our peer-to-peer applications with the metadata lessons learned from the Web?
The core of the World Wide Web Consortium’s (W3C) metadata vision is a concept known as the Semantic Web . This is not a separate Web from the one we currently weave and wander, but a layer of metadata providing richer relationships between the ostensibly disparate resources we visit with our mouse clicks. While HTML’s hyperlinks are simple linear paths lacking any obvious meaning, such semantics do exist and need only a means of expression.
Enter the Resource Description Framework (RDF), a data model and XML serialization syntax for describing resources both on and off the Web. RDF turns those flat hyperlinks into arcs, allowing us to label not only the endpoints, but the arc itself—in other words, ascribe meaning to the relationship between the two resources at hand. A simple link between Andy Oram’s home page and an article on the O’Reilly Network provides little insight into the relationship between the two. RDF disambiguates the relationship: “Andy wrote this particular article” versus “this is an article about Andy” versus “Andy found this article rather interesting.”
RDF’s history itself shows how emerging peer-to-peer applications can benefit from a generalized and consistent metadata framework. RDF has roots in an earlier effort, the Platform for Internet Content Selection , or PICS. One of ...