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The W3C found many problems with HTML. There was a need to define other HTML like languages to handle different network documents. As a result, the W3C defined the Extensible Markup Language or XML. Below are some key features.

In effect, XHTML - bridges the gap between HTML and XML

XML Basics

XML (eXtensible Markup Language) is an Internet standard for representation of information content. A subset of SGML (Standard Generalized Markup Language), XML is a metalanguage for defining an unlimited number of markup languages. Each of these languages can contain an unlimited number of tags.

"XML defines a specific method for creating text formats for data so that files are program independent, platform independent, and support internationalization (able to be read in different languages, etc.). In fact, because XML is an extensible language, you don't even have to have a browser to interpret the page. Applications can parse the XML document and read the information without any human intervention. XML, unlike HTML, is concerned with the identity, meaning, and structure of data (text and pictures). XML is extensible because it lets Web site developers create their own set of customized tags for documents. This ability to define your own tags is the main feature of XML, and it is what gives developers more flexibility. By defining your own markup tags, you can explicitly define the content in the document. This makes XML a more intelligent markup language than HTML." Miller, Dick R. (2000) XML: Libraries' Strategic Opportunity. Library Journal Net Connect.

We won't be doing much with XML, but you might be interested in learning more about it. Try the following activity. What is the difference between the two following types of markup?

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<h1>Pickeled Prunes</h1>

<p>Source: The Joy of Cooking</p>
<p>3 cups water</p>
<p>1 cup cider vinegar</p>
<p>2 cups brown sugar</p>
<p>2 cups dried prunes</p>
<p>1 teaspoon whole cloves</p>
<p>1 teaspoon whole allspice</p>
<p>1 1/2 sticks cinnamon</p>

<ol>
<li>Simmer 45 minutes.</li>
<li>Place the prunes in a jar.</li>
<li>Strain out the spices.</li>
<li>Pour the liquor over the prunes.</li>
</ol>

<p>Keep refrigerated</p>

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<recipe>

<recipetitle>Pickeled Prunes</recipetitle>

<source>Source: The Joy of Cooking</source>
<ingredient>3 cups water</ingredient>
<ingredient>1 cup cider vinegar</ingredient>
<ingredient>2 cups brown sugar</ingredient>
<ingredient>2 cups dried prunes</ingredient>
<ingredient>1 teaspoon whole <spice>cloves</spice></ingredient>
<ingredient>1 teaspoon whole <spice>allspice</spice></ingredient>
<ingredient>1 stick <spice>cinnamon</spice></ingredient>

<steps>
<step1>Simmer 45 minutes.</step1>
<step2>Place the prunes in a jar.</step2>
<step3>Strain out the spices.</step3>
<step4>Pour the liquor over the prunes.</step4>
</steps>

<warning>Keep refrigerated</warning>

</recipe>

XML DOM

DOM, short for Document Object Model, is the specification for how objects in a Web page (text, images, headers, links, etc.) are represented. The DOM defines what attributes are associated with each object, and how the objects and attributes can be manipulated. In other words, DOM determines how an XML document will be accessed, manipulated, and displayed.

DHTML, short for Dynamic HTML, uses the DOM to dynamically change the appearance of pages after they have been downloaded to a user's browser.

For years web developers have had to deal with the different proprietary object models of Netscape and Internet Explorer. The W3C produced a DOM level 1 (DOM1) in 1998 and finalized it in late 2000. The latest version is now DOM2. Netscape 6.x and Internet Explorer 5.5 and above began to embrace the new standard. Other browsers (Opera and Mozilla, for example) are popular partly because they are designed to be standard-compliant. Although some differences among the browsers' adoptions of the standard may still exist, it is more possible today than at any time to code without having to cater to proprietary formats. The chances for true interoperability on the Web have come closer.

To learn more about DOM, read the Document Object Model page from wikipedia.

Complete the XML DOM Tutorial at W3Schools. Explore XML DOM Examples from W3Schools.

In brief, the DOM is a map of all objects found on a Web page starting with the browser window at the top of the hierarchy. The document object is thus one level below the the window object. And the document itself has objects.

window.document.form

Use this link to view the DOM of your browser (by Mike Hall): DOM viewer

Examples

Here are some samples of how you can combine your knowledge of HTML, CSS, and JavaScript to write DHTML.

sample 1 - Aligning text

sample 2 - Underlining text

sample 3 - Creating background color

sample 4 - Changing font family

sample 6 - Changing the background color of a table cell

sample 7 - Making text disappear

sample 8 - Making text change color

sample 10 - Changing the background color of noncontiguous text (variation of sample 9)

sample 11 - Changing the background color of noncontiguous text (variation of sample 9)

CHALLENGE: Modify and/or combine some of the preceding scripts to make a real-life usage. For example:

Learn More

XML

DOM


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