Types of URLs

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There are several different types of URLs. The one we have currently seen in this paper is the HTTP URL. When the World Wide Web, and its Web browser, was first introduced to the Internet, in late 1993, it offered an easy, single, consistent user interface that could be used to browse, or view, text and graphics at the same time. With the introduction of the Web was a new server known as the HTTP server.

Prior to the introduction of the HTTP server, there were several other servers already in use on the Internet. These servers allowed user to --

To work with the different types of resources found on the Internet, you need a way to tell your browser how to find the resource and the type of resource you want to work with. It can be a file that you want to download, a news article you want to read, or a gopher site that has a menu that you want to view. Each type of resource will reside on its own type of server.

NOTE: Different types of servers

To review the types of Internet servers see the section Servers of the Internet section found earlier in this paper.

There are many different types of URLs, however the most common schemes are: 





  HTTP URLs



HTTP is the Internet protocol specifically created for the World Wide Web, thus it will be the most common scheme you are likely to use.  These are the HyperText documents of the World Wide Web.  HTTP, as pointed out previously,
stands for HyperText Transport Protocol.  HTTP servers are commonly used for storing and serving hypertext documents.  These types of documents tend to be extremely efficient, containing navigational information within themselves.  Moving from one
document to another is handled via an embedded reference this means that the server protocol does not have to contain support for navigational features like Gopher or FTP protocols require.


For instance, you may want to go to a page that gives you information on creating a home page, you can enter an address like:

             http://www.goliath.org/makepage/index.html




This URL is the 'Welcome to "Make Your Own Home Page"' page.  Notice that it is an HTTP type URL.


HTTP URLs have become the most common type of URLs on the Net today.



  File Transfer Protocol (FTP) URLs



FTP URL scheme is used to access files and directories on Internet hosts using the FTP protocol.  The FTP protocol is one of the oldest was of transmitting files over the Internet.  While there are many advantages to using HTTP
instead, many servers don't offer the full support of HTTP.  In addition, many client programs are developed for FTP. This is especially true if you are accessing the Internet via Terminal emulation as many UNIX clients still do.  In addition, many files
are distributed only via FTP on the Internet.


Connecting to an FTP site works basically the same way as logging into an HTTP site.  For example, to connect to the Internet’s 'Electronic Frontier Foundation' computer, you would use the URL:

                ftp://ftp.eff.org/


Notice that the URL is very similar to an HTTP URL.  Instead of specifying the type of server as http://, you specified ftp://.  The name of the site where the resource is located is ftp.eff.org/.  Notice in this case that you
ended the URL with a forward slash.  This ftp does not specify a specific path and document name.  Therefore, it displays the contents of the sub-directory pointed to on the ftp server.


Another example will specify a specific file that you want to locate.  Once located, your browser will either display it, if it recognizes the format or notify you that it doesn’t recognize the format and offer to save it to disk for you.  If you want to
find and display the file named cda_approved.gif on the same ftp server we just connected to, you would enter the following URL:

             ftp://ftp.eff.org/pub/EFF/Graphics/cda_approved.gif


Your browser will display a graphic similar to the following:








  

     click to view in separate window ==>> 
     
   See picture<<==
click to load here
    
  









Notice that the above URL looks very similar to the URLs that you have specified when working with HTTPs.  In this  case it has a directory and file name as part of the URL.


    
NOTE: Case sensitivity


    
 Notice that the above URL has both lower and upper case in the URL name.  URLs are case sensitive and must be entered exactly the same as the case sensitivity of the directory and file names.





  Gopher URLs



As you work with FTP URLs you begin to realize ftp sites can be very frustrating to work with.  You have to remember all of those ftp site names and, oh, many of the ftp sites have weird directory and file names.  This is where a
gopher URL can help.  Gophers (and WAISs) are essentially menu systems.  They take a request for information and then scans the Net for it.  This eliminates the need for you to have to search for it.  Once a menu is displayed, you can select files and
programs from ftp sites for downloading or displaying.


The Gopher protocol syntax is very similar to FTP and HTTP.  Instead of using http:// or ftp:// you specify gopher://.  For example, to connect to the National Cancer Center gopher site in Tokyo, Japan, the URL is:

        gopher://gopher.ncc.go.jp/


Or another site you may be interested in is the United Nations Criminal Justice Country Profiles gopher site.  This site is maintained at the Albany, NY university.  The gopher URL is:

          gopher://UACSC2.ALBANY.EDU:70/11/newman


Once on the server, you will see a menu similar to this one:








  

     click to view in separate window ==>> 
     
   See picture<<==
click to load here
    
  









This menu is actually looking at a Gopher server.  Notice that it is a series of menus choices.  Since you are using a browser, like Netscape, it shows all the choices as underlined text.


To select any of the choices all you have to do is double mouse click on the menu choice you want.


Using this Gopher menu, you can click on the UN Criminal Justice Country Profiles and then select any country whose information you want to review or copy.


    
WARNING : It asks for a port # when connecting to a FTP or GOPHER server!


    
 Sometimes, you may have to specify a port number for the FTP or Gopher site you are trying to connect to. Usually it will default OK with a port number.   If you are connecting to a FTP or GOPHER site via a browser and a menu choice on another
Web document, the port number will be passed at the same time, automatically.





  News URLs



The final most common type of URL used is to connect to an Usenet newsgroup.  These URLs are known as News URLs.


Before demonstrating how to connect to a News URL, we need to quickly discuss UseNet:




    
Note : What is USENET


    
USENET is a large collection of computers that share data with each other.  It is the people that use these computers that make USENET worth the effort.  Imagine a conversation that is being carried on over days, where anyone can put their
two-cents in.  Usenet is like email, except that it is many-to-many instead of one-to-one.  It is the international meeting place where people gather to meet their friends,  discuss events, or talk about anything they want.  Often, many people believe
that USENET is the Internet.  However, it is a totally separate system.  All Internet sites CAN carry Usenet.  Usenet has millions of messages posted each day -- it is HUGE.




The basic building block of the Usenet is the newsgroup which is a collection of messages related to a theme.  There are almost 10,000 of these newsgroups, in a wide range of languages, covering any subject you can imagine.  Which Usenet groups
you have access to depends upon your Internet service provider.  Each newsgroup usually has a fee attached to it and requires that the provider pay this fee.  Therefore the services available are those that your provider subscribes to.


To connect to a newsgroup you use its URL.  Unlike the previous URLs, you do not specify the new service the same way you connect to other URLs.  Specifically, you do not specify the double forward slashes.


Before you use any news services, you will have to specify the news server used by your Internet provider.  In Netscape this is done via specifying your NNTP (Net News Transfer Protocol) server in the Preferences dialog box, under the Options box.  In
Mosaic you set an environment variable NNTPSERVER to the name of the news server.  Most browsers will let you set the news server via a file menu choice like options.


Once your news server has been specified, you can point to a Usenet newsgroup by referencing the URL.  For instance, to connect to the US jobs offered newsgroup you would type:

      news:us.jobs.offered



  Other URLs



There are several other URLs that you can reference from your browser.  Each can be referenced similar to the way you have worked with HTTP, FTP and GOPHER URLs.


Some of the other URLs you may come across are:




Although you may not come in contact with these URLs often, you may find them as links in other WWW documents.  For instance, if you see a link like “send message to page owner” it will probably use a MAILTO URL.  Some URLs like Telenet will require that
you have a Telenet application linked to your browser.  Since Telenet allows you to login to a server as a terminal, you will need some sort of program that lets you act as a terminal.  This application will run by your browser when you log into the
server.








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