Often, a single URL may need to correspond to different resources. Take the case of a web site that wants to offer its content in multiple languages. If a site such as Joe's Hardware has both French- and English-speaking users, it might want to offer its web site in both languages. However, if this is the case, when one of Joe's customers requests "http://www.joes-hardware.com," which version should the server send? French or English?

Ideally, the server will send the English version to an English speaker and the French version to a French speaker-a user could go to Joe's Hardware's home page and get content in the language he speaks. Fortunately, HTTP provides content-negotiation methods that allow clients and servers to make just such determinations. Using these methods, a single URL can correspond to different resources (e.g., a French and English version of the same web page). These different versions are called variants.

Servers also can make other types of decisions about what content is best to send to a client for a particular URL. In some cases, servers even can automatically generate customized pages-for instance, a server can convert an HTML page into a WML page for your handheld device. These kinds of dynamic content transformations are called transcodings. They are done in response to content negotiation between HTTP clients and servers.

In this chapter, we will discuss content negotiation and how web applications go about their content-negotiation duties.

 

Hypertext Transfer Protocol (HTTP)