Web clients and servers use the HTTP protocol [RFC2616] to request representations of Web documents and send back the responses. HTTP has a powerful mechanism for offering different formats and language versions of the same Web document known as content negotiation. When a user agent (such as a browser) makes an HTTP request, it sends along some HTTP headers to indicate what data formats and language it prefers. The server then selects the best match from its file system or generates the desired content on demand, and sends it back to the client. [...] RDF/XML, the standard serialisation format of RDF, has its own content type, application/rdf+xml. Content negotiation thus allows publishers to serve HTML representations of a Web document to traditional Web browsers and RDF representations to Semantic Web-enabled user agents. This also allows servers to provide alternative RDF serialisation formats like Notation3 [N3] or TriX [TriX].