Tự học HTML và CSS trong 1 giờ - part 14 doc

If you’re linking files on a personal computer Macintosh or PC, and you want to link to a file on a different disk, use the name or letter of the disk as just another directory name in t

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example, include directions to go up two directory levels and then go down two other

directories to get to the file

To specify relative pathnames in links, you must use UNIX-style paths regardless of the

system you actually have You therefore separate directory or folder names with forward

slashes (/), and you use two dots to refer generically to the directory above the current

one ( )

Table 6.1 shows some examples of relative pathnames and where they lead

TABLE 6.1 Relative Pathnames

href=”file.html” file.html is located in the current directory.

href=”files/file.html” file.html is located in the directory called

files, and the files directory is located in the current directory.

href=”files/morefiles/file.html” file.html is located in the morefiles

directory, which is located in the files directory, which is located in the current directory.

href=” /file.html” file.html is located in the directory one

level up from the current directory (the parent directory).

href=” / /files/file.html” file.html is located two directory levels up,

in the directory files

If you’re linking files on a personal computer (Macintosh or PC), and you want to link to

a file on a different disk, use the name or letter of the disk as just another directory name

in the relative path

Absolute Pathnames

You can also specify the link to another page on your local system by using an absolute

pathname

Absolute pathnames point to files based on their absolute locations on the file system.

Whereas relative pathnames point to the page to which you want to link by describing its

location relative to the current page, absolute pathnames point to the page by starting at

the top level of your directory hierarchy and working downward through all the

interven-ing directories to reach the file

Absolute pathnames always begin with a slash, which is the way they’re differentiated

from relative pathnames Following the slash are all directories in the path from the top

level to the file you are linking

106 LESSON 6: Adding Links to Your Web Pages

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Table 6.2 shows some examples of absolute pathnames and what they mean

TABLE 6.2 Absolute Pathnames Examples

directory /u1/lemay (typically on UNIX systems).

href=”/d|/files/html/file.htm” file.htm is located on the D:

disk in the directory files/html (on Windows systems).

href=”/Macintosh%20HD/HTML Files/file.html” file.html is located on the disk

Hard Disk 1 , in the folder HTML Files (typically on OS X systems).

Using Relative or Absolute Pathnames?

The answer to that question is, “It depends.” If you have a set of files that link only to

other files within that set, using relative pathnames makes sense On the other hand, if

the links in your files point to files that aren’t within the same hierarchy, you probably

want to use absolute links Generally, a mix of the two types of links makes the most

sense for complex sites

Let’s say that your site consists of two sections, /stuffand/things If you want to link

from the file index.htmlin/stufftohistory.htmlin/stuff(or any other file in

/stuff), you use a relative link That way, you can move the /stuffdirectory around

without breaking any of the internal links On the other hand, if you want to create a link

in/stuff/index.htmlto/things/index.html, an absolute link is probably called for.

That way, if you move /stuffto/more/stuff, your link will still work.

The rule of thumb I generally use is that if pages are part of the same collection, I use

relative links, and if they’re part of different collections, I use absolute links

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Top has different meanings, depending on how you publish your HTML files If you just link to files on your local disk, the top is the top of your file system ( / on UNIX, or the disk name on a

Macintosh or PC) When you publish files using a web server, the top is the directory where the files served by the web server are stored, commonly referred to as the document root You learn more about absolute pathnames and web servers in Lesson 20,

“Putting Your Site Online.”

NOTE

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▼

Links to Other Documents on the Web

So, now you have a whole set of pages on your local disk, all linked to each other In

some places in your pages, however, you want to refer to a page somewhere else on the

Internet—for example, to The First Caesars page by Dr Ellis Knox at Boise State

University for more information on the early Roman emperors You also can use the link

tag to link those other pages on the Internet, which I’ll call remote pages Remote pages

are contained somewhere on the Web other than the system on which you’re currently

working

The HTML code you use to link pages on the Web looks exactly the same as the code

you use for links between local pages You still use the <a>tag with an hrefattribute,

and you include some text to serve as the link on your web page Rather than a filename

or a path in the href, however, you use the URL of that page on the Web, as Figure 6.5

shows

Task: Exercise 6.2: Linking Your Caesar Pages to the Web

Go back to those two pages you linked together earlier, the ones about the Caesars The

menu.htmlfile contains several links to other local pages that provide information about

12 Roman emperors

Now suppose that you want to add a link to the bottom of the menu file to point to The

First Caesars page by Dr Ellis Knox at Boise State University, whose URL is

http://www.boisestate.edu/courses/westciv/julio-cl/

First, add the appropriate text for the link to your menu page, as follows:

The First Caesars page by Dr Ellis Knox has more information on

these Emperors.

What if you don’t know the URL of the home page for The First Caesars page (or the

page to which you want to link), but you do know how to get to it by following several

links on several different people’s home pages? Not a problem Use your browser to find

the home page for the page to which you want to link Figure 6.6 shows what The First

Caesars page looks like in a browser

FIGURE 6.5

Link to remote

files.

URL of remote file

Closing tag

< A H R E F = " h t t p : / / w w w c e r n c h / " > C e r n H o m e P a g e < / A >

Opening tag

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You can find the URL of the page you’re currently viewing in your browser in the

address box at the top of the browser window To find the URL for a page you want to

link to, use your browser to go to the page, copy the URL from the address field, and

paste it into the hrefattribute of the link tag No typing!

After you have the URL of the page, you can construct a link tag in your menu file and

paste the appropriate URL into the link, like this:

”<a href=”http://history.boisestate.edu/westciv/julio-cl/”>

The First Caesars</a>” page by Dr Ellis Knox has more information on these

Emperors.

In that code I also italicized the title of the page using the tag You’ll learn more

about that tag and other text formatting tags on Lesson 7, “Formatting Text with HTML

and CSS.”

Of course, if you already know the URL of the page to which you want to link, you can

just type it into the hrefpart of the link Keep in mind, however, that if you make a

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FIGURE 6.6

The First Caesars

page.

If your system isn’t connected to the Internet, you might want to connect now so that you can test links to pages stored on the Web.

NOTE

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▼

mistake, your browser won’t find the file on the other end Many URLs are too complex

for humans remember them; I prefer to copy and paste whenever I can to cut down on

the chances of typing URLs incorrectly

Figure 6.7 shows how the menu.htmlfile, with the new link in it, looks when it displays

Task: Exercise 6.3: Creating a Link Menu

Now that you’ve learned how to create lists and links, you can create a link menu Link

menus are links on your web page that are arranged in list form or in some other short,

easy-to-read, and easy-to-understand format Link menus are terrific for pages that are

organized in a hierarchy, for tables of contents, or for navigation among several pages

Web pages that consist of nothing but links often organize the links in menu form

The idea of a link menu is that you use short, descriptive terms as the links, with either

no text following the link or with a further description following the link itself Link

menus look best in a bulleted or unordered list format, but you also can use glossary lists

or just plain paragraphs Link menus enable your readers to scan the list of links quickly

and easily, a task that might be difficult if you bury your links in body text

In this exercise, you create a web page for a set of book reviews This page serves as the

index to the reviews, so the link menu you create is essentially a menu of book names

FIGURE 6.7

The First Caesars

link.

▲

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Start with a simple page framework: a first-level heading and some basic explanatory

text:

<!DOCTYPE html><html>

<head>

<title>Really Honest Book Reviews</title>

</head>

<body>

<h1>Really Honest Book Reviews</h1>

I read a lot of books about many different subjects Though I’m not a

book critic, and I don’t do this for a living, I enjoy a really good read

every now and then Here’s a list of books that I’ve read recently:

Now add the list that will become the links, without the link tags themselves It’s always

easier to start with link text and then attach actual links afterward For this list, use a tag

to create a bulleted list of individual books The <ol>tag wouldn’t be appropriate

because the numbers would imply that you were ranking the books in some way Here’s

the HTML list of books, and Figure 6.8 shows the page as it currently looks with the

introduction and the list:

<ul>

<li>The Rainbow Returns by E Smith</li>

<li>Seven Steps to Immeasurable Wealth by R U Needy</li>

<li>The Food-Lovers Guide to Weight Loss by L Goode</li>

<li>The Silly Person’s Guide to Seriousness by M Nott</li>

</ul>

</body>

</html>

Now, modify each of the list items so that they include link tags You need to keep the

<li>tag in there because it indicates where the list items begin Just add the <a>tags

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FIGURE 6.8

A list of books.

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around the text itself Here you link to filenames on the local disk in the same directory

as this file, with each individual file containing the review for the particular book:

<ul>

<li><a href=”rainbow.html”>The Rainbow Returns by E Smith</a></li>

<li><a href=”wealth.html”>Seven Steps to Immeasurable Wealth by R U.

Needy</a></li>

<li><a href=”food.html”>The Food-Lovers Guide to Weight Loss by L.

Goode</a></li>

<li><a href=”silly.html”>The Silly Person’s Guide to Seriousness by M.

Nott</a></li>

</ul>

The menu of books looks fine, although it’s a little sparse Your readers don’t know

any-thing about each book (although some of the book names indicate the subject matter) or

whether the review is good or bad An improvement would be to add some short

explanatory text after the links to provide hints of what is on the other side of the link:

<ul>

<li><a href=rainbow.html”>The Rainbow Returns by E Smith</a> A”

fantasy story set in biblical times Slow at times, but interesting.</li>

<li><a href=”wealth.html”>Seven Steps to Immeasurable Wealth by R U.

Needy</a> I’m still poor, but I’m happy! And that’s the whole point.</li>

<li><a href=”food.html”>The Food-Lovers Guide to Weight Loss by L Goode

</a> At last! A diet book with recipes that taste good!</li>

<li><a href=”silly.html”>The Silly Person’s Guide to Seriousness by M.

Nott</a> Come on who wants to be serious?</li>

</ul>

The final list looks like Figure 6.9

You use link menus similar to this one throughout this book

FIGURE 6.9

The final menu

listing.

▲

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Linking to Specific Places Within

Documents

The links you’ve created so far in this lesson have been from one point in a page to

another page But what if, rather than linking to that second page in general, you want to

link to a specific place within that page—for example, to the fourth major section down?

You can do so in HTML by creating an anchor within the second page The anchor

cre-ates a special element that you can link to inside the page The link you create in the first

page will contain both the name of the file to which you’re linking and the name of that

anchor Then, when you follow the link with your browser, the browser will load the

sec-ond page and then scroll down to the location of the anchor (Figure 6.10 shows an

example.)

Anchors are special places that you can link to inside documents Links can then jump to

those special places inside the page as opposed to jumping just to the top of the page

You can use links and anchors within the same page so that if you select one of those

links, you jump to a different anchor within the page For example, if you create an

anchor at the top of a page, you could add links after each section of the page that return

the user to the top You could also create anchors at the beginning of each section and

include a table of contents at the top of the page that has links to the sections

Creating Links and Anchors

You create an anchor in nearly the same way that you create a link: by using the <a>tag

If you wondered why the link tag uses an <a>rather than an <l>, now you know: a

actu-ally stands for anchor.

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FIGURE 6.10

Links and anchors.

softfruits.html berries.html

Please choose a subtopic:

Soft Fruits

*Strawberries

*Cane Fruits:

*Bush Fruits:

*Blackberries

*Raspberries

*Loganberries

*Blueberries

*Huckleberries

Strawberries are an herbaceous plant

Strawberries

Blackberries

Blueberries

Blackberries grow on canes

Blueberries grow on bushes

in colder climates

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When you specify links by using <a>, the link has two parts: the hrefattribute in the

opening<a>tag, and the text between the opening and closing tags that serve as a hot

spot for the link

You create anchors in much the same way, but rather than using the hrefattribute in the

<a>tag, you use thenameattribute The nameattribute takes a keyword (or words) that

name the anchor Figure 6.11 shows the parts of the <a>tag when used to indicate an

anchor

Including text between the anchor tags is optional The actual anchor is placed at the

location of the opening anchor tag, so you can just as easily write it as follows:

The browser scrolls the page to the location of the anchor so that it’s at the top of the

screen

For example, to create an anchor at the section of a page labeled Part 4, you might add

an anchor called part4to the heading, similar to the following:

<h1><a name=”part4”>Part Four: Grapefruit from Heaven</a></h1>

Unlike links, anchors don’t show up in the final displayed page They’re just a marker

that links can point to

To point to an anchor in a link, use the same form of link that you would when linking to

the whole page, with the filename or URL of the page in the hrefattribute After the

name of the page, however, include a hash sign (#) and the name of the anchor exactly as

it appears in the nameattribute of that anchor (including the same uppercase and

lower-case characters!), like the following:

<a href=”mybigdoc.html#part4”>Go to Part 4</a>

This link tells the browser to load the page mybigdoc.htmland then to scroll down to the

anchor named part4 The text inside the anchor definition will appear at the top of the

screen

FIGURE 6.11

anchors.

< a name="Part4">Part Four: Planting Corn</a>

Text that will be at the top of the screen Anchor name

to link to

Closing tag Opening tag

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▼ Task: Exercise 6.4: Linking Sections Between Two Pages

Now let’s create an example with two pages These two pages are part of an online

refer-ence to classical music, in which each web page contains all the referrefer-ences for a

particu-lar letter of the alphabet (a.html,b.html, and so on) The reference could have been

organized such that each section is its own page Organizing it that way, however, would

have involved several pages to manage, and many pages the readers would have to load if

they were exploring the reference Bunching the related sections together under lettered

groupings is more efficient in this case (Lesson 18, “Writing Good Web Pages: Do’s and

Don’ts,” goes into more detail about the trade-offs between short and long pages.)

The first page you’ll look at is for M; the first section looks like the following in HTML:

<!DOCTYPE html><html>

<head>

<title>Classical Music: M</title>

</head>

<body>

<h1>M</h1>

<h2>Madrigals</h2>

<ul>

<li>William Byrd, This Sweet and Merry Month of May</li>

<li>William Byrd, Though Amaryllis Dance</li>

<li>Orlando Gibbons, The Silver Swan</li>

<li>Claudio Monteverdi, Lamento d’Arianna</li>

<li>Thomas Morley, My Bonny Lass She Smileth</li>

<li>Thomas Weelkes, Thule, the Period of Cosmography</li>

<li>John Wilbye, Sweet Honey-Sucking Bees</li>

</ul>

Secular vocal music in four, five and six parts, usually a capella.

15th-16th centuries.

See Also

Byrd, Gibbons, Lassus, Monteverdi, Morley, Weelkes, Wilbye 

</body

</html>

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