XML- HTML - XHTML introduction

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Introduction

SGML

In 1986 the Standard Generalized Markup Language (SGML)  became an international standard for defining descriptions of the structure and content of different types of electronic documents. SGML, the "mother tongue" of HTML and XML, is used for describing thousands of different document types in many fields of human activity, from transcription  of ancient Sumerian tablets to the technical documentation for stealbombers, and from patient's clinical records to musical notations.

SGML has withstood the test of time. Its popularity is rapidly increasing among organizations with large amounts of document data to create, manage, and distribute as in the Defense, Aerospace, Semiconductor and Publishing industries. However, various barriers exist to delivering SGML over the Web. These barriers include the lack of widely supported stylesheets, complex and unstable software because of SGML’s broad and powerful options, and obstacles to interchange of SGML data because of varying levels of SGML compliance among SGML software packages.

These difficulties have condemned SGML to being a successful niche technique  rather than a mainstream tool. Indeed some cynics have renamed SGML in 'Sounds Good Maybe Later'.

 

HTML
HTML is a subset of SGML, the most frequently used document type in the Web. It defines a single, fixed type of document with markup that lets you describe a common class of simple office style report, with headings, paragraphs, lists, illustrations, etc., and some provision  for hypertext and multimedia.

HTML was defined to allow the transfer, display and linking of documents over the internet and is the key enabling technology for the WWW. Prior to the emerging of the internet, it was unusual in the word of computing to hear the word "page" used to describe elements of data. But HTML web pages have amazing similarities with paper in their role of information publishing. Both HTML and paper pages

are optimized for visual clarity,
focus on ultimate usability (but not on reusability),
contain no contextual information, and
have no document structure to enable automation.
Today's web is created by Hand for Eyes only. HTML has too low an "Information IQ" to enable many desirable applications. HTML was designed as a  markup language an with simple structures, strong emphasis on formatting and  was weak for encoding content.  It was not designed to encode structure and semantics needed for complex applications.

 

XML
Because of the lack of SGML support in mainstream Web browsers, most applications that deliver SGML information over the Web convert the SGML to HTML. This down-translation removes much of the intelligence of the original SGML information. That lost intelligence virtually eliminates information flexibility and poses a significant barrier to reuse, interchange, and automation.

For this reason, XML (Extensible Markup Language) was developed by the XML working group (known as the SGML Editorial Review Board) formed under the auspices of the World Wide Web Consortium (W3C) in 1996. XML is a highly functional subset of SGML. The purpose of XML is to specify an SGML subset that works very well for delivering SGML information over the Web. When the mainstream Web browsers support XML, it is believed that it’s going to be very easy to publish SGML information on the Web. It's actually misnamed because XML is not a single Markup Language. It is a metalanguage to let users design their own markup language.

XML is a public format and not a proprietary format of any company. The v 1.0 specifications was accepted by the W3C as Recommendation on February 10, 1998.

XML was conceived as a means of regaining the power and flexibility of SGML without most of its complexity. While retaining the beneficial features of SGML, XML removes many of the more complex features of SGML that make the authoring and design of suitable software both difficult and costly. But XML also lacks some important capabilities of SGML that primarily affect document creation, not document delivery. That’s because XML was not designed to replace SGML in every respect.

The question that is open is not whether XML will succeed as a widespread data format, but rather how fast, to what level of success and with what products. The question of whether XML would enter the market was answered when Microsoft, Adobe, Netscape and other big market players not only supported the development of the new standard but began making sizable product investments to this new format. The leading Web browser Products already support XML in their latest releases. The momentum building behind the XML effort means that XML is inevitably destined to become the mainstream technology for powering broadly functional and highly valuable business applications on the Internet, intranets, and extranets.

 

XHTML
XHTML is a working draft for there formulation of HTML 4.0 [HTML] as an application of XML 1.0 [XML]. It is the basis for a family of future document types that extend and subset HTML.

There are two major reasons for content developers to adopt XHTML. First, XHTML is designed to be extensible (Design you own tags). Second, XHTML is designed for portability. There will be increasing use of non-desktop user agents to access Internet documents. Some estimates indicate that by the year 2002, 75% of Internet document viewing will be carried out on these alternate platforms. In most cases these platforms will not have the computing power of a desktop platform, and will not be designed to accommodate ill-formed HTML as current user agents tend to do. Indeed if these user agents do not receive well-formed XHTML, they may simply not display the document.

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XML- some facts
Many voices in the industry say, that XML will revolutionize the exchange of business information similar to the way the phone, fax machine, and photocopier did when those devices were invented.
 

The XML Working Group

The XML Working Group consists of about 14 companies and organizations with a strong interest in either providing or utilizing XML tools. This group includes Adobe, ArborText, DataChannel, Fuji Xerox, Hewlett-Packard, Inso, Isogen, Microsoft, Netscape, SoftQuad, Sun Microsystems, and the University of Chicago, along with   W3C representatives and independent experts. Most of the Working Group members bring considerable experience with SGML to the task of defining and refining XML. The Working Group of the World Wide Web Consortium (W3C) ensure the highest possible degree of utility and interoperability.


XML Goals
The Goals of XML are defined (by the XML W3C Working Group) in the XML Specifications as:

XML shall be straightforwardly usable over the Internet.
XML shall support a wide variety of applications.
XML shall be compatible with SGML.
It shall be easy to write programs which process XML documents.
The number of optional features in XML is to be kept to the absolute minimum, ideally zero.
XML documents should be human-legible and reasonably clear.
The XML design should be prepared quickly.
The design of XML shall be formal and concise.
XML documents shall be easy to create.
Terseness in XML markup is of minimal importance.
 

General Fields of application
XML has some essential benefits: It is system-independent, vendor independent, proven with HTML on the Web. XML provides advanced maintainable linking. XML has metadata markup and is delivered via the Web. There are style sheets for views, transforms, information presentation. XML enables integration of legacy systems with Web enabled SME’s, and provides end to end document flow with smart process control. Centralized repositories of information, documents, rules, structures and formats, as well as loosely coupled distributed systems are other business impacts of XML. General Fields of application are:

XML-based protocols can interoperate, such as VoxML, the voice recognition protocol, with the banking industry's Open Financial Exchange protocol, which facilitates the exchange of financial data between financial institutions, businesses, and consumers. Banks, for example, can build personal financial management applications that can use voice recognition simply by adding a few lines of XML code, instead of incorporating an entire voice recognition application into the financial software.

With XML-specific tags, search engines can give users more refined search results. A search engine seeks the term in the tags, rather than the entire document, giving the user more precise results.

Web authors can approach content creation more strategically with XML than with HTML. When they create a document, they can use the XML metadata tag to think about how other people will consume and access that document.

XML can make electronic data interchange (EDI) transactions accessible to a broader set of users. EDI is already a powerful tool that has been deployed by large organizations around the globe to exchange data and support transactions. But today, EDI transactions can only be conducted between sites that have been specifically set up to exchange information using compatible systems. XML will allow data to be exchanged, regardless of the computing systems or accounting applications being used. XML should create new possibilities for how data is used, and there are many initiatives under way to move EDI to XML.

Microsoft is considering using XML as Exchange's native file format to speed access to/from the message store. This step is needed if Exchange is to be able to handle 5 million users on a clustered NT environment, 2 or 3 years from now. By building upon these types of XML mechanisms, XML/EDI can leverage these tools, such as workflow, cataloging, routing and searching.

Enterprise resource planning (ERP) heavyweights such as PeopleSoft Inc., Oracle Corp., and SAP AG plan to incorporate XML syntax into products to help companies lower the cost and labor involved in exchanging data with business partners. Separately, third-party software vendors are pushing XML to enable data exchange over the Web between separate financial systems.

...and many more!

 

Momentum behind XML has grown at a startling rate since development of the XML specification began September of 1996:

Microsoft Internet Explorer 5.0 already supports XML.
Netscape future Browser Gecko will also support XML.
Furthermore, every major database tool by end of 1999 will be XML.
Microsoft Visual Developer now supports XML.
The Multimedialanguage SMIL will also be adopted by major companies.
It’s very likely that all the companies represented in the XML Working Group will either support or utilize XML within the next year.
Articles about XML frequently appear in mainstream IT publications.
XML is likely to become the underlying technology for powering intranets and extranets, which leverage the power of the Internet for serious business applications.