Notice: This material is excerpted from Special Edition Using HTML, 2nd Edition, ISBN: 0-7897-0758-6. This material has not yet been through the final proof reading stage that it will pass through before being published in printed form. Some errors may exist here that will be corrected before the book is published. This material is provided "as is" without any warranty of any kind.
by John Jung
As you learned in Chapter 4, "Building Blocks of
HTML," putting a link in your home page to someone else's page
is pretty easy. But now you're ready for something more advanced: linking
your page to other resources on the Internet. The World Wide Web is just
one of many resources on the Net; creating links to others is important.
You don't always need to link your home page, but knowing how is good if
you ever want to do it. Fortunately, creating links to other resources
on the Net through your
home page is very easy.
The World Wide Web is a popular part of the entire
Internet, but many
others resources are available. Most of them were around long before the
Web was even born, and as a result, they have a lot of stuff on them. Also
as a result of the Web's newness, the other resources sometimes have a
much wider audience base. Whether you're designing a home page for yourself
or for your company, you may want to know how to link to those resources.
These resources can take various shapes, from the peanut gallery that
is
Usenet news to personal
e-mail to the capability to access other computers
through
Telnet. Although you can create your own versions of these resources
using forms (see Part IV, "Forms and CGI"), most of the time
you wouldn't want to do so. For example, you could easily create a page
with many HTML form tags, text elements, and a submit button for e-mail,
but simply creating a link to e-mail with a particular address would be
easier. This way, you can more easily update the page because you don't
have to worry about which forms to read. Also, sometimes browsers have
built-in support for some of the other resources, giving the user faster
response time.
You especially want to create links to other resources on the Net if
you're already using a resource. If you already have a Gopher site with
information that's updated automatically, why rebuild it to fit the Web?
Just adding a hyperlink to your Gopher site makes more sense. Similarly,
if you're running a
BBS that's on the
Internet, putting in a Telnet link
to it makes more sense. There's no reason for re-creating, or even mirroring,
your BBS through forms for the Web.
The single most popular activity on the Internet is sending
e-mail.
More people use e-mail than any other resource on the Net. The reason is
quite simple: If you're on the Internet, you have an e-mail address. The
provider that gives you access to the Net often has at least one e-mail
program available for your use. Most modern e-mail programs offer a friendly
interface, with no complex commands to learn.
You'll most likely want to put in an e-mail link when you want people
to give you feedback on a particular topic. Whatever it is you want comments
on-be it your home page or your company's product-if you want to know what
people think, use an e-mail link. E-mail links are also useful for reporting
problems, such as a problematic or missing link. Typically, the Web master
of a particular site should put these types of links to himself or herself.
You really have no reason not to put in a link to your e-mail address.
Creating a link to an e-mail address is similar to creating a link to
another
home page. The only difference is the reference point for your
anchor element. Normally, you put a link to a home page around some text
as in the following:
See Chapter 4, "Building Blocks of HTML," for information on the basic structure of the hyperlink.
<A HREF="http://www.mycom.com/myhome.html">Go to my home page</A>.
Linking to e-mail is just as simple. Instead of entering http, which specifies a home page, type mailto: to specify an e-mail address. And instead of specifying a URL, put in your full e-mail address. So the preceding example now looks like this:
<A HREF="mailto:me@mycom.com">Send me E-mail</A>.
The link created with the preceding HTML code will look like any other
hypertext link. You can easily mix and match hyperlinks to different resources,
and they'll all look the same (see fig. 7.1).
When this link is selected, the browser opens its own
e-mail interface
for the user. Each interface is different, but most of them automatically
get your e-mail address and real name, and prompt you for a subject.
E-mail links look just like regular
hypertext links.
If you're creating a Web page of limited distribution, you don't need to put in your entire e-mail address. This often occurs in very large companies or universities, where there are internally available Web pages. Instead of putting in your complete e-mail address, just use your username. So instead of putting in:
<A HREF="mailto:me@mysite.com">You'd use:
<A HREF="mailto:me">
Because the e-mail link is a standard URL and easily implemented, many
browsers have built-in support for it. As a result, when people click on
an e-mail link, the
Web browser will put up a primitive
mail program. A
few companies offer a full set of
Internet applications, from an e-mail
program, to a
newsreader, to a
Web browser. Oftentimes, these work in conjunction
with each other. Consequently, when you click on an e-mail link, these
Internet packages will start up their own
e-mail program (see
fig. 7.2).
Netscape will launch its own internal and full-featured e-mail program
when you click on an
e-mail link.
Usenet is one of the best, or worst, resources on the Net, depending on whom you ask. Anybody with an opinion can tell you what he thinks. That person may not know what he is talking about, but he can let you know what he thinks. Usenet is the ultimate embodiment of the freedom of speech, letting everybody say anything they want.
This ability of anybody anywhere on the Net having a voice could be
an asset to your home page. Often, you may want to put in a link to Usenet
when you want people to read for more information. If your home page has
some information about
HTML authoring, for example, you might want readers
to go to a particular newsgroup for more help. You can also include such
a link so that people can see what differing opinions are. If you have
a certain political view and want others to see what the opposition is,
a Usenet news link would be helpful.
Creating a link to a Usenet newsgroup is pretty simple; this kind of
link is also just a derivative of the basic
hypertext link. As you did
with the e-mail link, you need to modify two parts in the anchor reference.
When you're creating a Usenet link, enter news: instead of http:.
Likewise, instead of specifying a particular URL, you put in a specific
newsgroup, as follows:
For more information, see <A HREF="news:news.newusers.questions">news.newusers.questions</A>.
As you can see in figure 7.3, the Usenet
news hyperlink looks identical to other links. When a user selects such
a link, the browser tries to access the user's Usenet news server. If the
news server is available to that person, the browser then goes to the specified
newsgroup. The user can then read as much as he or she likes in that particular
group.
Usenet news links allow you to make a point to people interested
in your topic.
When a user clicks on a Usenet news link, his or her browser tries to access the newsgroup in question. Because it's this user's browser and environment, he or she might not have access to the group you specified. Not all
Internet providers have access to the same
newsgroups. When you're creating such links, be mindful that not everybody will necessarily be able to access them.
How a Usenet hyperlink is handled is left entirely up to the
Web browser
the person is using. Many of them treat each article in a newsgroup as
an individual hyperlink. Often, there's little in the way of sophisticated
newsreading features. Some companies, such as Netscape, offer an entire
suite of programs, including a Usenet newsreader (see
fig. 7.4). In these cases, the newsreading portion of that suite is
started up.
When a Usenet link is accessed, some sophisticated Web browsers will
start up their own internal
newsreader.
Another popular activity is accessing an FTP site. FTP, or File Transfer
Protocol, allows users to copy files from other computers (the FTP site)
onto their own computers. This popular method allows companies to distribute
their demo software or patches to their products.
Putting in a link to an FTP site allows users to get a specific file
from a particular location. This capability is useful for companies and
shareware authors in making their products available. This type of link
is also great for people who review software, allowing them to let users
get the files being reviewed. Also people who have files, such as FAQs
and interesting pictures, that they want others to get to easily might
want to put in a link to an FTP site.
You create a link to an FTP site the same way you create other links,
and they look the same, too (see fig. 7.5).
You enter ftp: instead of the usual http:, and you change
the URL address to //sitename. Simply put, the site name
looks the same as the URL address. You need to make sure that the site
name you specify points to a machine that accepts FTP connections.
FTP
links are almost always supported by the browser natively. You can create
A typical FTP link as follows:
You can get the FAQ <A HREF="ftp://ftp.mysite.com/pub/FAQ">here</A>.
An FTP link allows many people to access a particular file.
If you don't specify a particular file name, the browser will list the files in the directory you specified. This is particularly useful if you want the user to have access to multiple files. Programs available on multiple machines, or large files broken up into several chunks, typically fall into this category.
Technically speaking, there isn't too much of a difference between FTP
and the Web. As a result, Web browsers support
FTP links without needing
another program. The browsers will give you a list of the files in the
current directory, and indicate which ones are directories and which ones
are files (see fig. 7.6). If you click on
a directory, it'll change into that directory. If you click on a file,
the browser will directly download the file.
Web browsers will have no problems handling
FTP links by themselves.
If a lot of people are reporting that they can't access some of your FTP links, try finding others. This error usually comes up when you have an FTP link to a particularly busy FTP site. You should try and locate other (less busy) FTP sites that have the same file you're pointing to.
By default, when FTP links are activated, the
FTP connection that's made is known as anonymous
FTP. This means that the FTP site the user is trying to access doesn't care who the user is. All the anonymous
FTP site cares about is sending and receiving files to anybody who logs in with the username "anonymous." The password is often the e-mail address of the user, but this isn't necessary.
Anonymous FTP allows
software companies and the like to distribute their products to a very wide audience.
A non-anonymous
FTP is where the
FTP site is very particular about who can access it. To get access to a non-anonymous FTP site, you must have an account on the FTP site itself. Basically, you can't get in to a non-anonymous FTP site unless you're already in. This is probably the most widely used FTP site around, as many companies allow employees to
FTP into their own accounts.
You can easily change an anonymous FTP link into a non-anonymous one. Simply put a username and the "@" sign before the sitename. This will cause most Web browsers to automatically attempt to login as username. The browser will then prompt the user for the password for the
login id.
Before there was the World Wide Web, there was something known as Gopher.
It was originally designed by the University of Minnesota (the Golden Gophers)
as a way of making information that's spread out easily available. Gopher
has probably been the
Internet resource most affected by the Web, often
being superseded by it. The biggest difference between Gopher and the Web
is that it is very difficult for individual people to create their own
Gopher sites or holes.
Though Gopher sites are not as prevalent as they once were, they still
have a strong following. You can typically find Gopher sites at places
that dispense a lot of automated information. Although the site could often
easily be converted to HTML, it simply hasn't bothered to. This conversion
of Gopher data into usable
HTML code is typically the work of a programmer,
and often not worth the effort. Putting in an
HTML link to a
Gopher site
allows people browsing your page easy access to a great deal of information.
You can create a link to a Gopher hole by modifying the same two elements
of the anchor reference. Change the http: to gopher:, and
change the URL to //sitename. The site name must be a valid
Internet host name address. The link created looks like every other type
of
hypertext link (see fig. 7.7), and built-in
support is provided by most
Web browsers. A
Gopher hole link usually looks
something like the following:
For more information, go <A HREF="gopher://gopher.mysite.com">here</A>.
Links to Gopher holes are great for accessing large amounts of automated information.
Just like FTP,
Gopher is a
Net resource that is built into
HTML. Consequently,
most
Web browsers will support any links to a
Gopher site internally. That
is, you don't need a Gopher-specific application to go to a Gopher site,
the browser will take care of it for you. But just like FTP, the built-in
support for Gopher is often very bland (see
fig. 7.8).
There's only so much a Web browser can do to liven up the text-based Gopher resource.
WAIS stands for Wide Area Information System, which basically means
"lots of large databases that you can search through." WAIS was
specially designed by
WAIS Corp. as a way of accessing large amounts of
information. This capability is very different from what
Gopher and the
Web do in that
WAIS was intended to cover very large chunks of information.
Typically, databases that contained several million entries were considered
appropriate for
WAIS.
WAIS is typically accessed through a search engine because most people
don't want to plod through such large stores of information. When WAIS
was first introduced, custom front ends allowed easy access to a
WAIS database.
With the advent of the Web, however, most
WAIS databases now have
HTML
front ends to their databases (see fig. 7.9).
Now you can simply fill out a Web form and click a button, and the WAIS
search is underway.
Most WAIS databases are now searchable through
HTML forms.
You can create a link in your home page to a WAIS database as easily as do with all the other links. You have to modify the same two anchor reference elements to hold the correct information. Instead of using http:, enter the prefix wais:, and change the URL location to be the address of a WAIS database:
To search for a number in your area, click <A HREF="wais://wais.mysite.com">here</A>.
Most browsers don't have built-in support of
WAIS database searches. If you put in a link to one of these databases, be sure to include some sort of reference to where users can get a WAIS client. Of course, if the WAIS database you're pointing to has
HTML forms support, you don't need to worry about including such information.
The capability to access other computers is not something new to the
Web; it's been around for a long time. This access has always been achieved
with a UNIX program called
Telnet, which doesn't stand for anything in
particular. Telnet allowed people to try to log in to a remote machine,
much the same way some people access their Internet providers. The Web
allows for support of accessing remote machines through a
Telnet link to
a remote computer.
Usually, people trying to get on a secure system are the people for
whom you want to provide a Telnet link. People who provide access to a
private, Internet-accessible BBS will most likely want to put in a Telnet
link. Also, companies that offer a BBS for
customer support may want to
make use of link to a
Telnet site. Generally speaking, for most home pages,
you have little or no reason to include a link to a remote site.
As you might have guessed, creating a Telnet link to a remote site requires
modifying the
anchor reference element. You change the http: to
telnet:. You also need to change the URL part of the anchor reference
to hostname.
Hypertext links that refer to
Telnet sites look
the same as other links (see fig. 7.10).
A typical
Telnet link takes the following form:
Click <A HREF="wais://wais.mysite.com">here</A> to access our BBS.
Usually, only BBSs have a need for Telnet links.
Most
Web browsers do not support
Telnet activity natively. They typically depend on an external application to talk correctly to the remote machine. If you put in a link to Telnet to another site, be sure to also include some reference to a Telnet client.
There are a few operating systems have built-in
Telnet capability. Among the OS's that have this are Windows NT and UNIX.
Even though Telnet is a rather simple
Net resource, it's also a very
difficult one. Among the many problem are issues of how to display the
remote session and how to interpret keypresses. As simple as these problems
may appear, they're hard to implement in a Web browser. For these reasons,
most
Web browsers don't have support for
Telnet. Rather, they leave it
up to the individual person to find a Telnet program and set it up (see
fig. 7.11).
Most Web browsers don't support the
Telnet links internally, so you
need another program to access these links.
Some
Web browsers allow something extra in the
anchor reference. Simply add the username you want the person to login in as, followed by the "@" sign, before the sitename. So that instead of:
Access my <A HREF="telnet://mysite.com/">system!</A>You can have:
Access my <A HREF="telnet://john@mysite.com/>system</A>On those browsers that support this, the
Web browser will pop up a little notice. This notice tells the user what login name should be used to access the system.
You may be wondering how well these hypertext links work with each other.
The answer is: very well. Even though the links are different, they all
look and behave the same. This common behavior exists because of the anchor
reference that all hyperlinks use. Some may need client programs not built
in to a Web browser, but that's not a big deal. This identical look and
feel of various
hypertext links allow
home pages to have a consistent feel.
Consistency in a home page is important because it allows people to simply
"know" they're in your home page without looking at the current
URL.
The best thing you can do is to treat all hypertext links in the same manner, with slightly different formats. Just take the same basic anchors, add a reference, and put in the correct pointer to that reference (see table 7.1). As a Web author, you must always remember that each person looking at your home page could be using any browser available. No hard and fast rules about what resources all browsers will support even exist. Whatever resource you want to link to, though, try to include a link to a location where the user can get a client.
Table 7.1 Sample Formats for Creating Links
Link To... | What to Use | Sample Link |
---|---|---|
Another home page | http://sitename/ | http://www.mysite.com/ |
An e-mail address | mailto:address | mailto:me@mysite.com |
A Usenet newsgroup | news:newsgroupname | news:news.newusers.questions |
An FTP site | ftp://sitename/ | ftp://ftp.mysite.com/ |
A Gopher site | gopher://sitename/ | gopher://gopher.mysite.com/ |
A WAIS database | wais://sitename/ | wais://wais.mysite.com/ |
Another computer | telnet://sitename/ | telnet://bbs.mysite.com/ |
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