Most URLs contain (roughly) three parts: the protocol, the
host name, and the directory or filename (see figure 5.15)
FIGURE 5.15 URL parts.
The protocol is the way in which the page is accessed; that
is, the means of communication your browser use to get the file. If the
protocol to talk to the server. In order for a link to work, the host named in
the link must be running a server that supports the protocol that’s specified.
So if you use an ftp URL to connect to www.example.com, the link won’t work if
the serer isn’t running FTP server software.
The hostname is the address of the
computer on which the information is stored, like www.goole.com,ftp.aaple.com,
or www.alot.com.the same hostname can support more than one protocol, as
follows:
http://example.com
ftp://example.com
it’s one machine that offers two
different information services, and the browser will use different methods of
connecting to each. As long as all three serves are installed and available on
that system, you won’t have a problem.
The hostname part of the URL might
include a port number. The port number tells your browser to open a connection
using the appropriate protocol on a specific network port. The only time you’ll
need a port number in URL, is if the serve responding to the request has been
explicitly installed on that port. If the server is listening on the default
port, you can leave the port number out. This issue is covered in day 17,
“designing for the real world.”
If a port number is necessary is
necessary, it’s placed after the hostname but before the director, as follows:
http://my-public-access-unix.com:1550/pub/file
if the port is not included, the
browser tries to connect to the default port number associated with the
protocol in the RUL. The default port for HTTP is 80, so a link to http://www.example.com:/are
equivalent.
Finally, the directory is the
location of the file or other form of information on the host. The directory
does not necessarily point to a physical directory and file on the server. Some
web applications generate content dynamically, and just use the directory
information as an identifier. For the files you’ll be working with while
learning HTML, the directory information will point to files that exist on your
computer.
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