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Uniform Resource Locator Tutorial:
What is a URL?


 

A tutorial for Web newcomers about URLs and URIs, Uniform Resource Locators, Uniform Resource Indicators, and additional Internet addressing schemes... "

SCHEMES:
The basis for referring to resources on the Internet is the URL, Uniform Resource Locator. URL is pronounced as if you are spelling "U-R-L". Do not pronounce URL as "earl".

The URL is a string of characters uniquely identifying the source. (No two sources on the Internet can ever have the same URL).

The basic URL format for a Web page resource is

scheme://host:port/path

The filename is part of the path. The scheme for a Web page is http which stands for HyperText Transfer Protocol. (HyperText Transfer Protocol is an application level protocol used to facilitate the transmission of data to and from the Web server). The http is followed by a colon and two forward slashes.

http://

Not all Web page addresses have port numbers but of the few that do, the port number is preceded by a colon.

:80

The port number must never be omitted from the URL or the resource will not be retrieved and you will receive some type of error message.

The URL for this Web document is

http://www.hitmill.com/internet/url.html

Breaking the URL apart, you can see that the scheme, http, is first, followed by the colon and the two forward slashes. Next you see the host name (also called a domain name), www.hitmill.com/ followed by a single forward slash. Last, you see the path:

internet/url.html

This particular path indicates that the file named url.html is located inside a folder named internet. There is no slash or period or dot after the filename, url.html. Recall that the .html extension indicates "HyperText Markup Language". Some servers have a need to shorten the .html file extension to .htm. This means the same thing but when copying a URL, be sure to get it the exact way the the address is supposed to be, case-sensitive and all. Occasionally you will see an extension of .shtml. This is simply a designation extension indicating what is supposed to be a secure .htm or .html file.

ADDITIONAL SCHEMES:
Web browsers are capable of letting you view additonal resources of the Internet besides Web pages written in HTML and using the scheme http://. There are currently eleven defined schemes. For more information go to http://www.w3.org/Addressing/URL/4.1_Schemes.html for a very fine article from W3C about schemes. Familiarize yourself just with the most commonly used schemes for now and understand that other forms of addressing will play a role in the near future.

ftp://
FTP is an acronym for File Transfer Protocol, a protocol for moving one or more files from one computer to another computer. The addressing scheme for file transfer protocol begins with the letters ftp and is following by a colon and two forward slashes just like the scheme for http.

ftp://server:port/directory/file
 
Example:
ftp://ftp.someplace.com:1020/nicefile.exe

You use this scheme to download files from an ftp-server onto your computer. Both major browsers support the ftp addressing scheme.

If you are interested in searching ftp archives using a Web-based interface you may be interested in trying your search from

http://ftpsearch.ntnu.no/.

The following ftp site has a file named /HTML available for ftp download. You do not have to download it, as I merely use the following as an example of an ftp URL:

ftp://ftp.seismo.usbr.gov

When you view this ftp resource file you will be able to see more than one file listed. The file size was indicated at the search site mentioned above.

news:
The scheme news: is used to access UseNET newsgroups. There are literally thousands of newsgroup resources on the Internet. When using this scheme to address a newsgroup you must follow the word news with a colon and DO NOT use any forward slashes.
 
http://www.interbiznet.com/hunt/archives/searchingnews.html  is an excellent article with hyperlinks about searching newsgroups. A very good search engine for searching for a particular category of newgroup is DejaNews at http://www.deja.com/. The following newsgroup is about HTML.

news:alt.html

You will only be able to view and participate in the newsgroups which have been subscribed to by your server (ISP, Internet Service Provider). If you want to participate in a newsgroup not subscribed to, just ask your server if they could subscribe it. (See what is involved, if they are able to do this).


 


 

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