Uniform Resource Identifiers
According to the W3C’s information on addressing (http://www.w3.org/Addressing/), a Uniform Resource Identifier is defined as “The generic set of all names/addresses that are short strings that refer to resources.” A URL, Uniform Resource Locator, is defined as “An informal term (no longer used in technical specifications) associated with popular URI schemes: http, ftp, mailto, etc.”
Thus, when speaking of URIs in this book, I will refer exclusively to URLs. Let us examine all of the pieces of a URL using a hypothetical one. Refer to RFC 1808 for the official specification.
http://myname:[email protected]:80/mydir/myfile.html?myvar=myvalue#myfrag
| http | scheme (protocol) |
| myname | username (optional) |
| mypass | password (optional) |
| httphandbook.org | network location (host) |
| 80 | port (optional) |
| /mydir/myfile.html | path (resource) |
| myvar=myvalue | query string (optional) |
| myfrag | fragment (optional) |
Sometimes it is also helpful to dissect a more common example.
http://httphandbook.org/
| http | scheme (protocol) |
| httphandbook.org | network location (host) |
| / | path (resource) |
Although the scheme and path can be omitted in most modern Web browsers, they are still required for a correct URL. Browsers will simply assume the HTTP protocol and the root directory (/) when these are not specified.