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Web server concepts

Web servers present a virtual hierarchy of information to browser programs. This is the path part of a URL. Although the top of the virtual hierarchy is rooted in the physical file system hierarchy, the virtual hierarchy need not correspond directly to the physical organization of data. Servers can usually be configured to map parts of the virtual hierarchy to different areas of the physical file system, or to redirect the requests to other servers. The URL may also identify a program that returns information in the form of a document. Information in the URL after the part that identifies the program is passed to the program as data that may be evaluated and used to determine the content of the document generated.

Programs invoked by the Web server are referred to as gateways. How information is passed from the server to these programs is described in the Common Gateway Interface (CGI) specification. (See Section ).

The CERN server was the first Web server that could act as a proxy, with caching of documents. A proxy server can be asked to query other servers for resources. Browsers request documents from the proxy, giving the full URL, and the proxy server then requests the document from the true server. The browser and the true server do not need to be able to communicate directly. The proxy server can also create a cache of documents and deliver frequently requested documents from the cache, thus reducing external network traffic at the expense of local disk space. It can be useful to run a caching proxy server internally, even on individual workstations, as proxies can be cascaded. Cascading is a technique used to reduce the amount of traffic on the network, whereby a workstation browser requests a document from the local proxy. If the local proxy does not have the document in its cache, it sends a request to the site proxy. If the site proxy does not have the document in its cache it sends a request to the actual server, which may itself be part of another chain of proxies.

• The MIME Standard
• The Hypertext Transfer Protocol

Spinning the Web by Andrew Ford
© 1995 International Thomson Publishing
© 2002 Andrew Ford and Ford & Mason Ltd
Note: this HTML document was generated in December 1994 directly from the LaTeX source files using LaTeX2HTML. It was formatted into our standard page layout using the Template Toolkit. The document is mainly of historical interest as obviously many of the sites mentioned have long since disappeared.