HTML and CSS Reference
In-Depth Information
D
URLs
APPENDIX
A URL (uniform resource locator)
1
is a uniform way to refer to objects and services on
the Internet. Even novice users should be familiar with typing a URL, such as
http://www.htmlref.com, in a browser dialog box, to get to a Web site. However,
URLs can be used for far more than just retrieving a Web page and can be used to invoke
other Internet services, such as transferring files via FTP or sending e-mail. Despite its
potentially confusing collection of slashes and colons, URL syntax is designed to provide
a clear, simple notation that people can easily understand. The concepts in this section will
help you to better understand the syntax of URLs, which is key to linking documents in and
beyond a Web site.
N
OTE
The W3C often calls what end users term a URL a URI. The W3C is working from
a more advanced view of Web addressing discussed later in the chapter. For this discussion we
always use URL, which is more broadly understood. Interestingly the HTML5 specification
drops URI in favor of the more widely understood term URL.
Basic Concepts
To locate any arbitrary object on the Internet, you need to find out the following information:
1. First, you need to locate and access the machine on the network on which the object
resides. Locating the site might be a matter of specifying its domain name or IP
address, whereas accessing the machine might require a username and password.
2. After you access the machine, you need to determine the name of the desired file,
where the file is located, the position in the file as specified by a fragment identifier,
and what protocol will be used to retrieve the information or access the object.
In other words, a URL describes where something is and how it will be retrieved. The
where
is specified by the machine name, the directory name, the filename, and potentially more.
1
Some people call URLs “universal resource locators.” Except for a historical reference to “universal
resource locators” in documentation from many years ago, the current standard wording is “uniform
resource locator.”
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