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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
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
A non-anonymous
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
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
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
There are a few operating systems have built-in
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
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
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/ |
|
