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HTTP: The Definitive Guide by Brian Totty, Marjorie Sayer, Sailu Reddy, Anshu Aggarwal, David Gourley

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URL Shortcuts

Web clients understand and use a few URL shortcuts. Relative URLs are a convenient shorthand for specifying a resource within a resource. Many browsers also support "automatic expansion" of URLs, where the user can type in a key (memorable) part of a URL, and the browser fills in the rest. This is explained in Section 2.3.2.

Relative URLs

URLs come in two flavors: absolute and relative . So far, we have looked only at absolute URLs. With an absolute URL, you have all the information you need to access a resource.

On the other hand, relative URLs are incomplete. To get all the information needed to access a resource from a relative URL, you must interpret it relative to another URL, called its base .

Relative URLs are a convenient shorthand notation for URLs. If you have ever written HTML by hand, you have probably found them to be a great shortcut. Example 2-1 contains an example HTML document with an embedded relative URL.

Example 2-1. HTML snippet with relative URLs

<HTML>
<HEAD><TITLE>Joe's Tools</TITLE></HEAD>
<BODY>
<H1> Tools Page </H1>
<H2> Hammers <H2>
<P> Joe's Hardware Online has the largest selection of <A HREF="./hammers.html">hammers
</BODY>
</HTML>

In Example 2-1, we have an HTML document for the resource:

http://www.joes-hardware.com/tools.html

In the HTML document, there is a hyperlink containing the URL ./hammers.html. This URL seems incomplete, but it is a legal relative URL. It can be interpreted relative to the URL of the document in which it ...

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