National Center for Supercomputing Applications
A Beginner's Guide to HTML

Linking to Other Documents

The chief power of HTML comes from its ability to link regions of text (and also images) to another document. The browser highlights these regions (usually with color and/or underlines) to indicate that they are hypertext links (often shortened to  hyperlinks or simply links).  

HTML's single hypertext-related tag is <A>, which stands for anchor. To include an anchor in your document: 

 1. Start the anchor with <A . (There's a space after the A.) 
 2. Specify the document that's being pointed to by entering the parameter 
   HREF="filename" followed by a closing right angle bracket: > 
 3. Enter the text that will serve as the hypertext link in the current document. 
 4. Enter the ending anchor tag: </A>. 

Here is an sample hypertext reference: 

    <A HREF="MaineStats.html">Maine</A>

This entry makes the word "Maine'' the hyperlink to the document  MaineStats.html, which is in the same directory as the first document. You can link to documents in other directories by specifying the relative path from the current document to the linked document. For example, a link to a file NJStats.html located in the subdirectory AtlanticStates would be:

    <A HREF="AtlanticStates/NJStats.html">New Jersey</A>

These are called relative links. You can also use the absolute pathname of the file if you wish. Pathnames use the standard UNIX syntax. 

Relative Links Versus Absolute Pathnames

In general, you should use relative links, because 

 1. You have less to type. 
 2. It's easier to move a group of documents to another location, because the
   relative path names will still be valid. 

However, use absolute pathnames when linking to documents that are not directly related. For example, consider a group of documents that comprise a user manual. Links within this group should be relative links. Links to other documents (perhaps a reference to related software) should use full path names. This way, if you move the user manual to a different directory, none of the links would have to be updated.  

Uniform Resource Locator

The World Wide Web uses Uniform Resource Locators (URLs) to specify the location of files on other servers. A URL includes the type of resource being accessed (e.g., gopher, WAIS), the address of the server, and the location of the file. The syntax is:

scheme://host.domain[:port]/path/filename 

where scheme is one of 

file 
   a file on your local system, or a file on an anonymous FTP server 
http 
   a file on a World Wide Web server 
gopher 
   a file on a Gopher server 
WAIS 
   a file on a WAIS server 
news 
   an Usenet newsgroup 
telnet 
   a connection to a Telnet-based service 

The port number can generally be omitted. (That means unless someone tells you otherwise, leave it out.) 

For example, to include a link to this primer in your document, you would use 

    <A HREF = "http://www.ncsa.uiuc.edu/General/Internet/WWW/HTMLPrimer.html"> 
    NCSA's Beginner's Guide to HTML</A>

This would make the text "NCSA's Beginner's Guide to HTML'' a hyperlink to this document. 

For more information on URLs, look at 

WWW Names and Addresses, URIs, URLs, URNs, written by people at CERN
   http://info.cern.ch/hypertext/WWW/Addressing/Addressing.html

A Beginner's Guide to URLs, located on the NCSA Mosaic Help menu 
   http://www.ncsa.uiuc.edu/demoweb/url-primer.html

Links to Specific Sections in Other Documents

Anchors can also be used to move to a particular section in a document. Suppose you wish to set a link from document A and a specific section in document B. (Call this file documentB.html.) First you need to set up a named anchor in document B. For example, to set up an anchor named "Jabberwocky'' to document B, enter  

    Here's <A NAME = "Jabberwocky">some text</a>

Now when you create the link in document A, include not only the filename, but also the named anchor, separated by a hash mark (#). 

    This is my <A HREF = "documentB.html#Jabberwocky">link</A> to document B.

Now clicking on the word "link'' in document A sends the reader directly to the words "some text'' in document B. 

Links to Specific Sections Within the Current Document

The technique is exactly the same except the filename is omitted. 

For example, to link to the Jabberwocky anchor from within the same file (Document B), use 

    This is <A HREF="#Jabberwocky">Jabberwocky link</A> from within Document B.

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