Chapter: XML and Web Services : Building XML-Based Applications : Formatting XML for the Web

An Overview of XHTML - XHTML 1.1: Modularization

If the analogy of a bridge is used for XHTML 1.0, then possibly the analogy of an eleva-tor could be used for XHTML 1.1. XHTML 1.0 creates a bridge to easily span the gap between HTML 4 and XML 1.0 compliance. XHTML 1.1 creates an elevator for raising the level of conformance of XHTML 1.0. Once a series of Web pages have become XHTML 1.0 compliant, they are on the ground floor. There is nowhere to go but up!

An Overview of XHTML

Someday the Web will be standardized. All Web pages will be completely cross-platform compatible and will load faster. Also, work will get done more quickly (especially for us Web developers). However, the standardization of the Web is still over the horizon, and movement toward that goal is painfully slow. In order to help prepare for the future, the W3C organization introduced XHTML 1.0 as an official recommendation on January 26, 2000. XHTML is a step toward the goal of standardizing markup for the Web. It is also a step toward making the Web “XML compatible.” XHTML is an XML application. XHTML is a reformulation of HTML into an XML application. Therefore, HTML is made XML compatible and open to interaction with future XML technologies.

XHTML 1.1: Modularization

On April 10, 2001 the Modularization of XHTML became an official W3C organization recommendation.

XHTML modularization is a dissection of XHTML 1.0 into a collection of abstract mod-ules, with each module representing a specific type of XHTML functionality (such as an abstract module for defining XHTML tables or an abstract module for defining XHTML text formatting). Modules are implemented through the use of XML DTDs. XHTML modularization allows different modules to be “mixed and matched” together within XML DTDs in order to create XHTML subsets and extensions.

After making the Modularization of XHTML an official recommendation, the W3C moved quickly and on May 31, 2001, XHTML 1.1 (module-based XHTML) also became an official recommendation.

XHTML 1.1 is basically the reformulation of the XHTML 1.0 Strict DTD into a mod-ule-based document type. This new module-based document type is designed to be portable and easily applicable across a broad collection of clients and platforms. With the advent of XHTML 1.1, end-user device vendors will be able to create DTDs that specify specifically which XHTML modules their devices support. Each of the modules will be consistent and conform with the Modularization of XHTML recommendation. This ensures that although a vendor might only be using a subset of XHTML, the subset will completely conform with XHTML 1.1. Compatibility will always be ensured.

In this section, we will take a quick rundown of the changes that have been made from XHTML 1.0. We will then go into a more detailed look at modularization in XHTML and its main areas of divergence from XHTML 1.0. Finally, in the subsection on syntax and definitions, we will run down the modules that make up the Modularization of XHTML and XHTML 1.1 document type.

Changes from XHTML 1.0

As previously stated, XHTML 1.1 is basically a reformulation of the XHTML 1.0 Strict DTD into a module-based document type. Many of the facilities available in other XHTML 1.0 document types (Transitional and Frameset) are not available in XHTML 1.1. The same general rules for strict adherence from XHTML 1.0 apply in XHTML 1.1.

The main differences between an XHTML 1.0 Strict DTD and XHTML 1.1 (apart from being defined in modules) are summarized here:

All features that were deprecated have been completely removed in XHTML 1.1. Most of the removed features dealt with layout and formatting. The goal here is as much separation as possible between data structure and visual formatting. The strategy is to rely on style sheets for presentation.

For all elements, the lang attribute as been removed and replaced with the xml:lang attribute.

For the a and map elements, the name attribute has been removed and replaced with the id attribute.

The Ruby collection of elements has been added to the document type.

Listing 11.14 demonstrates a simple example of a document that conforms to XHTML 1.1. The code for this listing, simplexhtml11.HTML, can be downloaded from the Sams Web site.

LISTING 11.16 Simple XHTML 1.1 Document

<?xml version=”1.0” encoding=”UTF-8”?>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”>

<title>A Simple XHTML 1.1 Document</title> </head>

<body>

<p>This document valid according to the XHTML 1.1 DTD.</p> </body>

</html>

This listing is very similar to the ones you saw earlier in the section on XHTML 1.0. The main difference is that the Document Type Declaration references the XHTML 1.1 DTD. Of course, the XHTML 1.1 DTD defines a stricter set of validation standards. Notice also that the XML declaration is included. This is not strictly required but is always highly recommended.

Now, let’s delve a bit further into XHTML modularization.

Modularization of XHTML

The Web is becoming more and more pervasive. It is creeping into almost every aspect of our lives. The Web is on our cellular phones, handheld devices, automobiles, and televi-sions. Soon it will be on our appliances. HTML has become the content language that is most used by vendors developing new Web-enabled devices. However, the splintering of HTML into different supported features across different vendors, combined with the introduction of new extensions and the mingling of data structure and presentation, has rendered HTML less than optimal for this purpose.

XHTML 1.0 was introduced in order to reformulate HTML 4 into an XML application. This reformulation allows vendors to tap in to the ever-expanding myriad of XML tech-nologies. However, XHTML 1.0 still defines a pretty broad markup. It encompasses basi-cally all of HTML 4. Simpler devices have little use for (or are totally incapable of using) much of what is available in XHTML 1.0. XHTML 1.0 is not necessarily cross-platform compatible in its Transitional and Frameset DTDs. XHTML 1.0 is an XML application, but it is not extensible.

The Modularization of XHTML makes XHTML extensible. XHTML has been broken down into abstract modules. Each module represents a building block that can be com-bined with other building blocks to create unique subsets of XHTML. This means that content developers and vendors can define new document types comprised only of the modules they require for their application or device. These new document types are still fully conforming subsets of XHTML because they are derived directly from combina-tions of XHTML modules.

To take this a step further, developers and vendors can actually create hybrid document types that define their own element structure and still reference XHTML modules. Developers and vendors can, in effect, create their own markup languages by combining elements that they define with modules from XHTML.

XHTML Is Separated into Modules

XHTML 1.1 separates XHTML 1.0 into 20 different abstract modules. Table 11.1 shows the modules that XHTML has been broken into.

TABLE 11.1 XHTML 1.1 Modules

There is one additional module that has been added to the recommendation. The XHTML 1.1 DTD also uses the Ruby Annotation module. The Ruby Module and its contents have been added to the end of Table 11.1

Any XHTML 1.1 document that is validated against the XHTML 1.1 DTD will not be considered valid if it contains any element(s) not contained in one the modules listed in Table 11.1 or in the Ruby Annotation Module. In the next section, we will expand on this by covering strict conformance with XHTML 1.1.

Strict Conformance Is Required

Strict conformance of a document with XHTML 1.1 requires absolute adherence to the following criteria:

The document must conform to the definitions expressed in the XHTML 1.1 DTD. The XHTML 1.1 DTD may be referenced using the following Document Type Declaration:

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”>

The root element of the document must be <html>.

The <html> element must designate the XHTML namespace using the xmlns

attribute. The value of the attribute should always be http://www.w3.org/1999/xhtml.

• The Document Type Declaration must be made prior to the root element.

Now that we have covered the specifics of strict conformance, let’s see exactly which of XHTML 1.0’s features have been removed from XHTML 1.1.

Deprecated Features Have Been Removed

In XHTML 1.0, the name attribute of the a, applet, form, frame, iframe, img, and map elements was deprecated. In XHTML 1.1, this attribute has been completely removed.

In addition to removing the deprecated features from XHTML 1.0, XHTML 1.1 removes all the deprecated elements from HTML 4. The elements that were deprecated in HTML 4 are applet, basefont, center, dir, font, isindex, menu, s, strike, and u.

XHTML 1.1 attempts to make a clean break with much of the outdated features of HTML and moves to separate structure from presentation. This is getting us closer to the original intent of HTML. XHTML 1.1 will rely on style sheets for any special presenta-tion formatting.

So far, we have covered XHTML 1.0, which reformulates HTML into an XML applica-tion, and we have seen the Modularization of XHTML in our coverage of XHTML 1.1. However, because XHTML 1.1 is virtually unsupported at this point, you might be won-dering how alternative devices such as cellular phones and handheld devices are being supported currently. In the next section, you’ll see how XHTML Basic was created in order to provide an easy, stripped-down, modularized version of XHTML 1.0 for alterna-tive devices.

XHTML Basic

Based on the proposed recommendation (at the time) of the Modularization of XHTML, XHTML Basic became a W3C recommendation on December 19, 2000. XHTML Basic was based on a minimal set of XHTML modules in order to provide a subset of XHTML for the purpose of delivering XML-conforming content to alternative devices such as pagers, cellular phones, handheld devices, televisions, and so on. Most alternative devices are characterized by their limited processing power, bandwidth, and screen sizes. Therefore, a very streamlined markup is required in order to be able to provide content. There’s just no room for any type of complex interpretation of detailed code, and XHTML Basic was designed specifically to fit this need.

First, we are going to cover the recent history behind creating XHTML-based markup for alternative devices. Then we will look at the supported HTML features found in XHTML Basic. Finally, we will go over the modules that make up the XHTML Basic document type.

XHTML for Alternative Devices

The two previously existing HTML subsets that are designed for alternative devices are Compact HTML (CHTML) and Wireless Markup Language (WML). Both of these markup languages have strengths and some weaknesses. CHTML is not a recognized standard and is not XML compliant. However, it does have expanded support of colors, animations, and other rich display features. WML is a standard that is recognized as part of the Wireless Application Protocol, as implemented by the WAP Forum.

WML is also an XML 1.0 application. This, of course, means that WML is well formed, may be validated, and is open to XML technology applications. However, WML is not extensible. Although WML is an XML 1.0 application, it is defined with a fixed set of tags and may not be expanded upon.

Even though WML and CHTML are competing languages, they do have several features in common. They both support basic text features, hyperlinks and links to documents, basic forms, basic tables, images, and meta-information. It was from these common fea-tures that XHTML Basic was started. Both representatives of CHTML and WML took part in the formulation of the XHTML Basic standard. Shortly after XHTML Basic was approved as a recommendation, the WAP Forum announced that it would be adopting XHTML Basic in its WAP 2.0 release. On July 31, 2001 the WAP Forum made its 2.0 specification public with WML reformulated as a modularized subset of XHTML. This means that WML is now fully XHTML (and XHTML Basic) compatible. The idea of XHTML for alternative devices is taking hold.

So, what XHTML features are actually supported in XHTML Basic? The next section covers this topic.

Supported XHTML Features

The first thing that should be noted here is that XHTML Basic is extensible. This is an important supported feature from the Modularization of XHTML. Even though very lim-ited features are supported, it is possible for the XHTML Basic DTD to be expanded on by referencing other XHTML modules. For example, the Scripting Module could be ref-erenced to extend XHTML Basic to support scripting for alternative devices that are powerful enough to allow script processing.

Before going into the specifics of what is supported, let’s take a quick look at what is not supported by XHTML Basic. The style element is not supported. This is because exter-nal style sheets are the only supported style method (because many devices may not sup-port style sheets at all). The script and noscript elements are not supported. Many alternative devices have very limited processing power and attempting script processing is simply not practical or possible. Additionally, because many of these simple devices only display monospaced text, things like bidirectional text, boldfaced font, and other text extension elements are not supported.

There are quite a few things that are not supported! So, what is supported? Let’s take a look at the supported items now.

Text Support

Basic text formatting features are supported in XHTML Basic. These include simple text-formatting markup such as paragraphs, breaks, lists, and headers. Listing 11.17 gives an example of a simple XHTML Basic document using text formatting. The code for this listing, xhtmlbasic.HTML, can be downloaded from the Sams Web site.

LISTING 11.17 Simple Text Formatting in XHTML Basic

<?xml version=”1.0” encoding=”UTF-8”?>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML Basic 1.0//EN” “http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en” > <head>

<title>XHTML Basic text features</title> </head>

<body>

<h3>Some supported text features</h3>

<p>The following list represents several of the supported XHTML Basic text formatting.</p>

<ul>

<li>Lists</li>

<li>Paragraphs</li>

<li>Headings</li>

</ul>

</body>

</html>

Listing 11.17 is a very simple listing that demonstrates a valid XHTML Basic document. The first line contains the XML declaration. Then the Document Type Declaration is included and contains a public reference to the XHTML Basic DTD. The markup within the document is limited to the html root element, head, title, body, h3, p, ul, and li. You will find that this is very typical of an XHTML Basic document. They are simple and streamlined, as their intended clients, alternative devices, require.

Hyperlinks and Linking to Documents

Both normal hyperlinks and the link element are supported in XHTML Basic. The hyperlink is the most basic and central feature of linking content on the Web. Therefore, it must be included.

The inclusion of the link element allows for the linking of external documents to the Web page. This is also an important feature because it allows style sheets to be linked to the document. In XHTML Basic external style sheets are the main media for providing formatting to documents. Listing 11.18 provides a simple example of using a link ele-ment and a hyperlink in an XHTML Basic document. The code for this listing, basi-clink.HTML and mystylesheet.css, can be downloaded from the Sams Web site.

LISTING 11.18 Using Hyperlinks and the link Element in XHTML Basic

<?xml version=”1.0” encoding=”UTF-8”?>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML Basic 1.0//EN” “http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en” > <head>

<title>XHTML Basic hyperlinks and link elements</title>

<body>

<h3>XML Tutorial Web Sites</h3>

<p>Here are some good XML Web sites</p> <ul>

<li><a href=”http://www.xml101.com”>XML101.com</a></li> <li><a href=”http://www.w3schools.com”>W3Schools.com</a></li> <li><a href=”http://www.xhtmlguru.com”>XHTMLguru.com</a></li> </ul>

</body>

</html>

In this listing, we use the same type of text formatting features used in Listing 11.18. However, now we have added a link element in order to link to an external style sheet, and we have added hyperlinks to three really good XML tutorial sites. Notice in the link element, because this is an empty element, that we have added “/” before the closing “>”. This is consistent with the requirements of the XML 1.0 specification.

Table Support

Very basic tables are supported. Keep in mind that tables can be very difficult to display on small devices. Therefore, you should use tables sparingly. Limit their use to display-ing information that requires a tabular presentation. Avoid using tables for the entire page layout. Listing 11.19 shows how a table might be used in XHTML Basic. The code for this listing, basictables.HTML, can be downloaded from the Sams Web site.

LISTING 11.19 Using Tables in XHTML Basic

<?xml version=”1.0” encoding=”UTF-8”?>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML Basic 1.0//EN”

“http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en” > <head>

<title>XHTML Basic tables</title>

<body>

<h3>Today’s Weather Forecast</h3> <table>

<tr><td>Current Temp</td><td>77 F</td></tr> <tr><td>High Temp</td><td>85 F</td></tr> <tr><td>Low Temp</td><td>72 F</td></tr> </table>

</body>

</html>

This listing uses a very simple table structure to provide a layout for a weather forecast. Only the table, tr, and td elements are used. You really should try to keep it this simple due to the processing limitations and display limitations of the devices that will be load-ing your XHTML Basic pages.

Forms Support

Basic XHTML forms are supported. Similar to using tables in XHTML Basic, your use of forms should be very limited. File and image input types are not supported. Listing 11.20 shows a simple form in XHTML Basic. The code for this listing, basicforms. HTML, can be downloaded from the Sams Web site.

LISTING 11.20 Using Simple Forms in XHTML Basic

<?xml version=”1.0” encoding=”UTF-8”?>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML Basic 1.0//EN” “http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en” > <head>

<title>XHTML Basic Forms</title>

</head>

<body>

<h3>Please enter your name and email address</h3> <form method=”post” action=”anotherpage.asp”>

Name: <input type=”text” id=”txtName” name=”txtName” /> <br />

E-Mail Address: <input type=”text” id=”txtEMail” name=”txtEMail” /> <br />

</body>

</html>

In this example, you can see that the form is kept very simple. Only two types of input elements are used: text and submit. No special formatting is applied here either. In many cases, in a normal HTML page, a form will be laid out with a table. In XHTML Basic, as mentioned in the previous subsection, this would not be a good idea because it takes undue processing to render the table. Finally, notice that the empty elements are closed with the “/” symbol. At the end of this chapter, we will take a quick look at XForms. XForms will represent a more robust means for supporting user input on alter-nate devices in the future.

Style Sheet Support

The style element is not supported in XHTML Basic. The XHTML Basic recommenda-tion supports linking to include external style sheets. This is preferred because an exter-nal style sheet can be linked to and used by clients that support style sheets and ignored by clients that do not support style sheets. In XHTML Basic, the div and span elements may be used along with the class attribute to hook style information to the structure of the document. Listing 11.18 showed you how to use a link element to include an exter-nal style sheet. Listing 11.21 demonstrates using the div element to apply a style from an external style sheet using a class attribute. The code for this listing, basicdiv.HTML, can be downloaded from the Sams Web site.

LISTING 11.21 Using div to Apply Styles in XHTML Basic

<?xml version=”1.0” encoding=”UTF-8”?>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML Basic 1.0//EN” “http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd”> <html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en” > <head>

<title>XHTML Basic Style</title>

<body>

<div class=”SectionTitle”>Applying Style</div>

<div class=”SectionContent”>This is a demonstration of adding style to XHTML Basic</div>

</body>

</html>

In this listing is a link to an external style sheet: mystylesheet.css. In the body of the document, two div elements are used to format the text. Each div element has a class attribute that is used to reference a class in the style sheet (for the purposes of this exam-ple, we are assuming that the style sheet contains the classes SectionTitle and SectionContent). The appropriate formatting for each class will be applied to the text contained within each div element. This is assuming that the device viewing this page supports style sheets; otherwise, default formatting for that device will be applied.

Images Support

Yes, images are supported in XHTML Basic, but before you get too excited, think about how slowly those huge, image-laden pages load on your desktop browser. Now think about how that page would load on your handheld! Personally, I would recommend not even using images in your XHTML Basic page. If you do decide to use images, use them very sparingly and make them very small. In its WAP 2.0 specification, the WAP Forum supports the use of pictograms, which are tiny images (such as the smiley faces you often see on bulletin boards on the Internet) that can be used to convey some additional meaning. According to the WAP forum, pictograms are supported in order to enhance communication across language boundaries.

Now that we have gone over the main features supported in XHTML Basic, let’s take a look at the exact modules supported in XHTML Basic and the criteria used for XHTML Basic document conformance.

XHTML Basic Document

The XHTML Basic document type is composed of a set of XHTML modules. The included modules are listed in Table 11.2.

TABLE 11.2 XHTML Basic Modules

A document that meets the requirements of XHTML Basic is a strictly conforming docu-ment. In order to be considered a strictly conforming document, the following criteria must be met:

The document must validate against the XHTML Basic DTD, which is comprised of the modules listed in Table 11.2.

The root element of the document must be <html>.

The root element must have the xmlns attribute with a value of

http://www.w3.org/1999/xhtml.

There must be a Document Type Declaration that references the XHTML Basic DTD. The XHTML Basic DTD can be found in the following location:

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML Basic 1.0//EN” “http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd”>

• The DTD subset must not be used to override any parameter entities in the DTD.

As long as these requirements are met, a document will be considered a conforming document.

So far in this chapter we have looked at some background on electronic data by covering DSSSL. Then we moved on to CSS and how they can be used to format HTML on the Web. We then looked at how CSS can be used to display XML on the Web. Next, we spent quite a bit of time covering what is going to be one of the centerpieces of data delivery and formatting on the Web in the future: XHTML. Before we wrap up this chap-ter, we are going to look at one more emerging XML technology: XForms. XForms is an XHTML-compatible application that is intended to replace HTML forms in the future.

Before going on to our coverage of XForms, however, let’s revisit Coca Cabana Technology Shop and see how they applied XHTML Basic to their Web site.

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XML and Web Services : Building XML-Based Applications : Formatting XML for the Web : An Overview of XHTML - XHTML 1.1: Modularization |