A Web page (also called a document) consists of objects. An object is simply a file—such as an HTML file, a JPEG image, a Java applet, or a video clip—that is addressable by a single URL. Most Web pages consist of a base HTML file and several referenced objects. For example, if a Web page contains HTML text and five JPEG images, then the Web page has six objects: the base HTML file plus the five images. The base HTML file references the other objects in the page with the objects’ URLs. Each URL has two components: the hostname of the server that houses the object and the object’s path name. For example, the URL
http://www.someSchool.edu/someDepartment/picture.gif
has www.someSchool.edu for a hostname and /some Department/ picture.gif for a path name. Because Web browsers (such as Internet Explorer and Firefox) implement the client side of HTTP, in the context of the Web, we will use the words browser and client interchangeably. Web servers, which implement the server side of HTTP, house Web objects, each addressable by a URL. Popular Web servers include Apache and Microsoft Internet Information Server.