How RDF and XML Are Related It doesn t take much imagination to realize that sending directed graphs across the Internet isn t, typically, a very practical solution. In order to express the RDF model (which we won t discuss in detail because the purpose of discussing RDF in this book is to help you understand its use in RSS 1.0) and send it across the wire, you need a way to serialize the RDF model. Serialization is the creation of a series of characters to represent the model. One way to do that is to serialize RDF as XML, which is called RDF/XML. All the RDF elements and attributes that you saw in RSS 1.0 documents or markup fragments are written in RDF/XML. You saw earlier that a URI is used in the arc of a directed graph. Having seen that, the way that parts of an RSS 1.0 document are related might now become clearer. Inside the channel element you will see an items element whose content represents the table of contents of an information feed: Each of the two rdf:li elements has a resource attribute that contains a URI. Somewhere else in the same document, you find the following markup relating to one item in the information feed:
http://www.XMML.com/2005/03/19.html This item describes what happened on March 19th. Putting this in terms of the RDF triple, you could say the following: The [item in the TOC] has a URI http://www.XMML.com/2005/03/19.html associated with [the content of an item element] I hope you can see that the connection expressed in the preceding two pieces of RSS 1.0 markup is an XML-based way of expressing the relationship between the item in the TOC and the item elsewhere in the information feed document. In other words, the URI in the rdf:resource and rdf:about attributes corresponds to the arc of an RDF directed graph. What RDF Is Used For RDF, as mentioned earlier, is intended to provide a framework for machine processing of resources on the Web. RDF can be used in many situations, including those in the following list: 115 RDF: The Resource Description Framework
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