XHTML - McGraw Hill Higher Education
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Transcript XHTML - McGraw Hill Higher Education
Comparing HTML,
XML, and XHTML
Ellen Pearlman
Eileen Mullin
Programming the Web Using XML
McGraw-Hill/Irwin
© 2004 by The McGraw-Hill Companies, Inc. All rights reserved.
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Learning Objectives
1. Trace the effect that the Web's immediate
popularity had on the development of
HTML, XML, and XHTML
2. Learn about the XML compatibility
requirements that differentiate an XHTML
document from earlier HTML ones
3. Discover how namespaces are used by
XML and XHTML documents
4. Learn about how XML manages documents
and data
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Hypertext and Hyperlinking
• The concept of hypertext – electronic linking
between documents stored on computer
systems – has been around nearly as long as
computer systems themselves.
• A graphic or text link on a Web page that
opens another Web page or document is
known as a hyperlink, and the act of following
a link to the intended destination is called
hyperlinking.
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The Origins of HTML
• HTML was originally created by Tim BernersLee, a physics researcher at the European
Center for Nuclear Research (CERN).
• Berners-Lee built a program to allow these
documents to be viewed and hyperlinked to
each other; programs like this are now known
as Web browsers.
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Web Protocols
• Berners-Lee also designed a set of
instructions (called a protocol) to tell a
browser what Web document to retrieve, how
to obtain it and how to display it.
• This protocol is called http (for HyperText
Transfer Protocol) and constitutes the
beginning part of most Web addresses (or
URL, short for Universal or Uniform
Resource Locator).
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Web Pages
• HTML documents are also commonly called Web
pages. The main entry point on an individual or
organization’s Web site is called the home page, and
usually takes as its filename index.html or index.htm.
• These file extensions (.html and .htm) tell the Web
browser that the file should be viewed as a Web page
using a Web browser, in the same way that a file
ending with .doc is an indicator that the file is a word
processing document that should be opened with
Microsoft Word.
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The Limitations of HTML
• As the Web rapidly gained in popularity,
HTML quickly proved inadequate to play host
to multimedia, games, and animation, and
forms processing.
• A committee of dedicated researchers
convened the World Wide Web Consortium
(W3C) to develop future incarnations of the
language.
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The Limitations of HTML (2)
• To accommodate continued user demands for
typographic and presentation controls, the
Cascading Style Sheets (CSS) standard was
introduced.
• However, the W3C concluded that what Web
developers truly needed was a metalanguage – a language for writing new Web
languages. This effort was what led to the
creation of XML.
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The Emergence of XML
• The W3C decided to develop a streamlined
version of SGML to serve the purpose of
linking many kinds of computer languages
together with a single tagging system.
• Named the Extensible Markup Language
(XML), it was designed to parallel HTML but
would let developers create and specify new
tags, structures, attributes, and other Web
language elements.
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Comparing HTML to XML
HTML
XML
<html>
<head>
<title>Memo</title>
</head>
<body>
<h2>To: Dorm Residents</h2>
<h2>From: Resident Advisor</h2>
<h2>Date: 11-17-03</h2>
<h2>Subject: Fire Hazards</h2>
<br>
<p>Boxes should not be stored in
hallways, stairwells, or against
doors. These areas must be clear
at all times.</p>
</body>
</html>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE correspondence SYSTEM
"Memo_template.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<filename>111703 Memo</filename>
<title>Memo</title>
<to>Dorm Residents</to>
<from>Resident Advisor</from>
<date>11-17-03</date>
<subjectFire Hazards</subject>
<message>Boxes should not be
stored in hallways, stairwells,
or against doors. These areas must
be clear at all times.</message>
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Comparing HTML to XML (2)
• Although HTML can display your data it really
doesn’t indicate what the information means
or how to use it.
• XML, on the other hand, is a markup
language that classifies the data it contains.
• One caveat is that XML is much stricter than
HTML about how well you code your markup.
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XML Technologies
• XML spurred development of a number of
robust technologies, including:
– Extensible Stylesheet Language (XSL)
– XML Schema
– Xpath
• When the W3C decided to reformulate HTML
based on XML rather than previous versions
of HTML, it led to the renaming of HTML as
Extensible Hypertext Markup Language
(XHTML).
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Taking the Mid-Road with XHTML
• XHTML was first released in early 2000 to
meet the needs of XML within Web pages. It
lets you create sets of markup tags for new
purposes. Its benefits include:
– Separating presentation markup from content.
– You can use XML tools and technologies with your
XHTML documents.
– XHTML 1.1 is modular: The parts of an XHTML
document can be divided into separate modules
and added or removed.
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XML’s Compatibility Requirements
• As an XML-based language, XHTML has
strict rules regarding its syntax.
– If you make mistakes in creating HTML code, most
Web browsers will strive to display the page as
best as possible anyway.
– Your page will not display at all within an XMLenabled browser if the XHTML syntax is flawed.
• Luckily, the syntax and coding rules of
XHTML are very easy to learn, and are truly
not that different from those of HTML.
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A Sample XHTML Document
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Creating an XHTML Document
• The tags that are needed in an XHTML
document describe:
– XML declaration, for indicating to the Web
browser what version of XML is at work
here.
– DOCTYPE declaration, which appears only
in a document that uses a document type
declaration (DTD).
– XML namespace
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XML Declarations
• All XML and XHTML documents begin with an
XML declaration that signals to XMLcompliant tools like editors and browsers that
they can process this document.
<?xml version="1.0" encoding="UTF-8"?>
• XML supports the Unicode character set,
which provides multilingual capabilities in
your XHTML or XML documents. UTF-8 is
one method of encoding Unicode characters.
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DOCTYPE Declaration and
Document Type Definition (DTD)
• The DOCTYPE declaration immediately follows the
XML declaration:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
• The most recent version of XHTML, called XHTML
1.1, uses a single XML document type, which too is
called XHTML 1.1.
• XHTML 1.0 uses three XML document types that
correspond to three DTDs: Strict, Transitional (the
one you’ll most likely use), and Frameset.
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XML Namespaces
• An XML namespace lets you distinguish which
definition you mean when you use certain tags.
<html xmlns="http://www.w3.org/1999/xhtml">
• For example, the tags <title> or <table> could either
be used in their HTML sense or when tagging a
listing of library records or furniture inventory.
• Specifying an XML namespace is the way to avoid
any confusion about what is meant by each tag
name.
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Reformulating an HTML Document
into HTML
• Add an XML declaration
• Add a DOCTYPE declaration to point to an
XHTML DTD
• Specify the XML namespace
• Clean up the HTML: Ensure tags are nested,
lowercase tags are used, closing tags and
empty elements are specified.
• In XHTML, quotes are required on attributes.
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XHTML Is Only Part of What You
Can Do on the Web With XML
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Choosing to Use XHTML or XML
• XHTML does not extend to you the full
potential of XML. XHTML represents just one
vocabulary of XML.
• XML has the ability to dynamically describe
the data that it transmits. Other languages
and tools are then needed to display and
reformat an XML document on the Web, or to
share its data with other applications.
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XHTML vs. XML: Choosing the
Right Language for the Job
• Use XHTML
– when you’re creating a display-only or
brochure-type Web site
– when you want to quickly publish your
documents on the Web
– when you’re redesigning a large set of
existing static HTML pages
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XHTML vs. XML: Choosing the
Right Language for the Job (2)
• Use XML
– to dynamically generate your content’s
presentation with different layouts and forms.
– to store your documents and data in a format
that’s searchable, reusable, and cross-platform.
– when you want your data to be able to interact
with applications.
– when you’re pursuing a “knowledge management”
strategy to make your organization’s information
accessible on demand
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Going Further with Namespaces
<?xml version="1.0" encoding="UTF-8"?>
<furn:furnishings
xmlns:furn="http://genuineclass.com/xml/homefurnishings/"
xmlns:xhtml="http://www.w3.org/1999/xhtml">
<xhtml:table>
<xhtml:tr>
<xhtml:td><furn:table material="walnut"
type="dining"/></xhtml: td>
<xhtml:td><furn:chair material="beech"
type="dining"/></xhtml:td>
<xhtml:td><furn:lamp material="iron" type="floor"/></xhtml:td>
</xhtml:tr>
</xhtml:table>
</furn:furnishings>
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Using a Default Namespace
<?xml version="1.0" encoding="UTF-8"?>
<furnishings
xmlns="http://genuineclass.com/xml/homefurnishings/"
xmlns:xhtml="http://www.w3.org/1999/xhtml">
<xhtml:table>
<xhtml:tr>
<xhtml:td><table material="walnut" type="dining"/></xhtml:td>
<xhtml:td><chair material="beech" type="dining"/></xhtml:td>
<xhtml:td><lamp material="iron" type="floor"/></xhtml:td>
</xhtml:tr>
</xhtml:table>
</furnishings>
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Purposes of XHTML and XML
• There are really two purposes for
XHTML and XML: managing documents
and data.
– In many cases, XHTML will be sufficiently
for publishing static, brochure-type
documents on the Web.
– Data applications, on the other hand, can
include a much wider assortment of uses,
and require XML’s flexibility.
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Data and Metadata
• One of the biggest problems the future may
hold for the Web is growth.
• One of the technologies currently in
development by the W3C to address this is
an XML vocabulary called the Resource
Description Framework (RDF).
• RDF is an XML-based language for
expressing metadata, which is data about
data.
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Summary
• Using XHTML is only the tip of the
iceberg that comprises the XML syntax.
• Using XHTML is a means of readying
your Web pages for the next generation
of Web browsers.
• Making your data available to other
applications will require you to work with
XML, rather than just XHTML.
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The End