Uniform Resource Locators
Last update on: 05-08-2008URL is a pointer to some bit of data on the Web, be it a web document, a file available via FTP, a posting on Usenet, or an email address. The URL provides a universal, consistent method for finding and accessing information.
In addition to typing URLs directly into your browser to go to a particular page, you also use URLs when you create a hypertext link within a document to another document. So, any way you look at it, URLs are important to how you and your browser get around on the Web.
URI/URL syntax in brief
Every URI (and therefore, every URL) begins with the scheme name that defines its name space, purpose, and the syntax of the remaining part of the URI. Most Web-enabled programs will try to dereference a URI according to the semantics of its scheme and a context-vbn. For example, a Web browser will usually dereference a http://example.org/ by performing an HTTP request to the host example.org, at the default HTTP port (see Port 80). Dereferencing the URI mailto:bob@example.com will usually start an e-mail composer with the address bob@example.com in the To field.
example.com is a domain name; an IP address or other network address might be used instead. In addition, URLs that specify https as a scheme (such as https://example2.com/) normally denote a secure web site.
The hostname portion of a URL, if present, is case insensitive (since DNS is specified to ignore case); other parts are not required to be, but may be treated as case insensitive by some clients and servers, especially those that are based on Microsoft Windows. For example:
- the links http://iteachweb.net and HTTP://ITEACHWEB.NET both will open same page.
- The link http://iteachweb.net/page_home.html is correct, but link http://iteachweb.net/PAGE_home.html will result in an HTTP 404 error.
understanding the web's lessons:
How The World Wide Web WorksWeb Browsers
Web Servers
Uniform Resource Locators