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Lecture 2: Adding Hypertext Links to a Web Page

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Learning Objectives

Create hypertext links between elements within a Web pageCreate hypertext links between Web pagesReview basic Web page structuresCreate hypertext links to Web pages on the InternetDistinguish between and be able to use absolute and relative pathnamesCreate hypertext links to various Internet resources, including FTP servers and newsgroups

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Creating a Hypertext Document

Hypertext documents contain hypertext links, items that you can select to view another topic or document, often called the destination of the link.

These links can point to:another section

the same document

to a different document

to a different Web page

to a variety of other Web objects

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Opening A Web Page

This figure shows that a browser may only show a portion of the web page. The user must scroll down to see the rest of the web page.

vertical scroll bar

horizontal scroll bar can also be shown

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Adding Hypertext Links

You can place hypertext links at the top of a web page to make it easier for the user to navigate to a particular section of the document instead of scrolling.

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How an Anchor Works

anchor

hypertext links

When the user clicks one of the hypertext links, the link will go directly to that section (anchor, which is the destination of the link) within the web page.

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Creating AnchorsThe <a> tag creates an anchor, text that is specially marked so that you can link to it from other points in a document.Text that is anchored is the destination of a link; it is not the text you click on.Each anchor has its own anchor name, using the “name” attribute i.e. <a name=“cc”>Classes</a>.An anchor doesn’t have to be text. You can mark an inline image as an anchor.Adding an anchor does not change your document’s appearance in any way. It merely creates locations in your Web page that become destinations of links.

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Creating LinksTo create a link to an anchor, use the same <a> tag you used to create the anchor.

The <a> tags used to create links are sometimes called link tags.

Use the href attribute, which is short for Hypertext Reference, to indicate the location to jump to.

href can refer to an anchor that you place in the document or to a different Web page or a resource anywhere on the Internet

it is important to note that the href attribute is case sensitive

You link to an anchor using the anchor name preceded by a pound (#) symbol i.e. <a href=“#gra”>Grading</a>.

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Creating Links Continued

After you create the anchors that serve as destinations for your links, you need to create the links themselves.

The <a> tag you use to create the anchor and the href attribute to indicate the location to jump to.

You should be careful to make each anchor name unique within a document.

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Text Links in the Browser

Text formatted as links

If the headings do not appear as text links, check your code to make sure that you are using the <a> and </a> tags around the appropriate text, the href attribute within the tag, and the quotes and # symbols.

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Web Page Structures

Storyboarding your Web pages before you create links helps you determine which structure works best for the type of information you’re presenting.You want to ensure that readers can navigate easily from page to page without getting lost.You’ll encounter several Web structures as you navigate the Web.Examining some of these structures can help you decide how to design your own system of Web pages.

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Linear Structures

In this structure you can jump only from one page to the next or previous page

Link to previous page

Link to next page

This figure shows one common Web page structure, the linear structure, in which each page is linked to the next and to previous page, in an ordered chain of pages.

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Augmented Linear StructureThis figure shows an augmented linear structure, in which you include a link in each page that jumps directly back to the first page, while keeping

the links that allow you to move to the next and previous pages.

first link jumps to previous page

second link jumps back to beginning

third page has three links

third link jumps to next page

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Hierarchical Structure

This figure shows the hierarchical structure, which starts with a general topic that includes links to more specific topics. Each specific topic includes links to yet more specialized topics, and so on.

In a hierarchical structure, users can move easily from general to specific and back, but not from specific to specific.

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XPHierarchical Structure on AltaVista Web Page

As with the linear structure, including a link to the top of the structure on each page gives users an easy path back to the beginning.

Subject catalogs such as the AltaVista directory of Web pages often use this structure. This figure shows this site, located at http://www.altavista.com.

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XPCombination of Linear and Hierarchical Structures

This figure shows a hierarchical structure in which each level of pages is related in a linear structure.

information about the play

the scenes

each level is linear

information about the acts

over

all s

truc

ture

is h

i era

rchi

cal

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Web Structures Continued

A little foresight can go a long way toward making your Web pages easier to use.

The best time to organize a structure is when you first start creating pages, when those pages are small in number and more easily managed.

If you’re not careful, your structure can become confusing and unmanageable for the user.

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Multipage Document with

No Coherent Structure

This structure is confusing, and it makes it difficult for readers to grasp the contents of the overall Web site. Moreover, a user who enters this structure at a certain page might not be aware of the presence of the other pages.

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XPCreating Links Among Documents

links to the conttxt.htm document,

which contains contact

information

links to the linktxt.htm document, which contains links to various Chemistry Web sites.

Unlike creating hypertext links between elements on the same page, this process does not require you to set an anchor in a file to link to it; the filename serves as the anchor or destination point.

the chem.htm document, which is the document containing the links.

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Linking to a Document

To create a link to a document, use the same <a> tag with the href attribute i.e. <a href=“contact.htm”>Contact me</a>.

In order for the browser to be able to locate and open contact.htm, it must be in the same folder as the document containing the link.

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XPHTML Code that Links to Other Documents

<a> tags to point to other

documents

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XPBrowser Displaying Links to Other Documents

links to the Contact and Links page

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XPLinking to a Section of a Document

To navigate to a specific location elsewhere in a document, rather than the top, you can set anchors and link to an anchor you create within the document.

for example, to create a link to a section in the Web page home.htm marked with an anchor name of “interests,” you create an anchor in home.htm in the section on Interests, and then enter the following HTML code in the current document:<a href=“home.htm#interests”> View my interests </a>• the entire text, “View my interests,” is linked to the Interests section in the

home.htm file, via the anchor name “interests”

• the pound symbol (#) in this tag distinguishes the filename from the anchor name

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XPAdding Links to Specific Locations in a Page

The pound symbol (#) in these tags (shown in red) distinguishes the filename from the anchor name.

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XPLinks in the Chemistry Page thatPoint to Anchors in the Links Page

links

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XPLinking to Documents in Other Folders

Browsers assume that if no folder information is given, the file is in the same folder as the current document.When referencing a file located in a different folder than the link tag, you must include the location, or path, for the file.HTML supports two kinds of paths: absolute paths and relative paths.

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Absolute Pathnames

An absolute pathname provides a precise location for a file.With HTML, absolute pathnames begin with a slash (/) and are followed by a sequence of folders beginning with the highest level folder and proceeding to the folder that contains the file.Each folder is separated by a slash.After you type the name of the folder or folders that contains the file, type a final slash and then the filename itself i.e. /tutorial.02/case/parks.htm.HTML also requires you to include the drive letter followed by a vertical bar (|) i.e. /C|/tutorial.02/case/parks.htm.

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Folder Tree

This figure shows five HTML files that are located in four different folders.

The top most folder is the tutorial.02 folder. Within the tutorial.02 folder are the tutorial and case1 folders, and within the case1 folder is the extra folder.

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Absolute Pathname

This figure shows absolute pathnames for five HTML files.

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Relative Pathnames

A relative path specifies the location for a file in relation to the folder containing the current Web document.As with absolute pathnames, folder names are separated by slashes.Unlike absolute pathnames, a relative pathname does not begin with a slash.To reference a file in a folder directly above the current folder in the folder hierarchy, relative pathnames use two periods (..) i.e. ../tutorial/chem.htm.

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Relative Pathnames Continued

Relative pathnames make your hypertext links portable.

Unlike absolute pathnames, If you move your files to a different computer or server, the hypertext links will stay intact.

If absolute pathnames are used, each link has to be revised. This can be a very tedious process.

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Relative Pathnames

This figure shows the relative pathnames and their interpretations for HMTL files and how they would be displayed.

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XPLinking to Documents on the Internet

To create a hypertext link to a document on the Internet, you need to know its URL.A URL, or Uniform Resource Locator, specifies a precise location on the Web for a file.You can find the URL of a Web page in the Location or Address box of your browser’s document window.Once you know a document’s URL, you can create a link to it by adding the URL to the <a> tag along with the href attribute in your text file i.e. <a href http://www.mwu.edu/course/info.html>Course Information</a>.

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XPUniform Resource Locator (URL)

Each URL follows the same format.The first portion of the URL identifies the communication protocol, which is a set of rules that governs how information is exchanged.

Web pages use the communication protocol HTTP, short for Hypertext Transfer Protocol, so all Web page URLs begin with the letters “http”.

Following the communication protocol, there is typically a separator, such as a colon and two slashes (://) i.e. http://www.mwu.edu.

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XPInterpreting Parts of a Uniform Resource Locator (URL)

This figure interprets a Web page with the URL http://www.mwu.edu/course/info.html#majors.

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Link to Another Page on the Web

As long as your computer is connected to the Internet, clicking the text within the tag navigates you to the document located at the specified URL.

Links to the College Board AP Internet page

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College Board AP PageChemistry page remains open in the original browser window

AP page in a separate browser

window

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Displaying Linked Documents

in a New Window

By default, each Web page you open is displayed in the main browser window, replacing the one you were viewing last.

To force a document to appear in a new window, instead of the main browser window, you would use the target attribute in the href tag i.e. <a href=“url” target=“new_window”>Hypertext</a>

url is the URL of the page, and new_window is a name assigned to the new browser window

the value use for the target attribute is used by the browser to identify the different open windows in the current browser session

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External Hyperlinks

You can set up external hyperlinks to open in the same browser window by using the same value for the target attribute.

if you do, the first hyperlink clicked opens the new window and displays the contents of the external file

as subsequent external hyperlinks are clicked, they replace the contents of the already opened window, and the contents of the main browser window remain unaffected

If you want your external documents to be displayed in their own browser window, you can assign a unique target value for each hyperlink, or you can assign the _blank keyword to the target attribute i.e. <a href=“url” target=_blank>Hypertext</a>.

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XPLinking to File Transfer Protocol (FTP) Servers

You can create links to other Internet resources, such as FTP (File Transfer Protocol) servers.

FTP servers can store files that Internet users can download, or transfer, to their computersFTP is the communications protocol these file servers use to transfer informationURLs for FTP servers follow the same format as those for Web pages, except that they use the FTP protocol rather than the HTTP protocol i.e. <a href= ftp://ftp.microsoft.com>Microsoft FTP server</a>.

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Displaying a FTP Site

Different browsers can display the contents of an FTP site in different ways. This figure shows what it might look like with Internet Explorer.

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Linking to Usenet News

Usenet is a collection of discussion forums called newsgroups that let users exchange messages with other users on a wide variety of topics.

The URL for a newsgroup is news:newsgroup.

To access the surfing newsgroup alt.surfing, you place this line in your HTML file i.e. <a href=news:alt.surfing>Go to the surfing newsgroup</a>.

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XPAccessing the alt.surfing Newsgroup

When you click a link to a newsgroup, your computer starts your newsgroup software and accesses the newsgroup.

This figure shows an example of the Outlook Newsreader program.

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Linking to E-mailMany Web designers include their e-mail addresses on their Web pages, so that users who access the page can send feedback.You can identify e-mail addresses as hypertext links.

when a user clicks the e-mail address, the browser starts a mail program and automatically inserts the e-mail address into the “To” field of the outgoing message

The URL for an e-mail address is mailto:e-mail_address.To create a link to the e-mail address davis@mwu.edu, the following code would be entered <a href=mailto:davis@mwu.edu>davis@mwu.edu</a>

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Mail Message Window

window opens when the

davis@mwu.edu link is clicked

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Adding an Email Link

the address itself is in the code for the mailto: URL

mail message window opens

with e-mail address already inserted

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Summary• Learned how to work with hypertext links.

• Learned how to create anchors within a Web page.

• Created links to anchors.

• Created hyperlinks within a single document and links to other Web pages.

• Discussed creating hyperlinks to resources other than Web pages, such as FTP sites, e-mail addresses and Gopher servers.