What is XML (Extensible Markup Language)?

INTRODUCTION

The Extensible Markup Language (XML) is the universal format for structured documents and data on the Web. - W3C XML Web site. 2000-07-06.

The Extensible Markup Language (XML) is descriptively identified within the XML 1.0 W3C Recommendation as a particularly simple dialect [or subset'] of SGML" the goal of which is to enable generic SGML to be served, received, and processed on the net within the way that's now possible with HTML" that reason "XML has been designed for simple implementation, and for interoperability with both SGML and HTML". 

Note that the "HTML" referenced in the preceding sentence (bis) means HTML 4.0 and 3.2 which were in common use as of 10-February 1998. When the XML 1.0 specification was published as a W3C Recommendation. The next version of "HTML is predicted to be reformulated as an XML application, in order that it'll be based upon XML instead of upon SGML. As of December 1998. "Voyager was the W3C code name for HTML reformulated as an application of XML.

WHAT IS XML?

EXtensible Markup Language (XML) may be a thanks to apply structure to an internet page. XML provides a typical open format and mechanisms for structuring a document in order that it are often exchanged and manipulated.

If you are familiar with HyperText Markup Language (HTML) it will be easier to learn that XML. In fact, XML complements your HTML knowledge by allowing you to structure your data by "marking-up" the text and data to define the info content. 

Like HTML, XML uses tags to "markup" data content. Unlike HTML. in XML you define your own tags that meet the precise needs of your document. The custom tags make your data easier to arrange and search.

XML will not change the way of your web page look, but it will change the way the documents are ead and the way the documents are filed and stored.

MARKUP LANGUAGE

Markup gives meaning to a document. This is something you do everyday like highlighted text, check marks on a bank statement, etc. If we would like others to know what markup means, we'd like a group of rules to declare what constitutes markup and declaring exactly what it means,

A markup language is not a formatting language. It is also not a programming language because programming language creates a set of instruction that is interpreted into a program.

Information Byte

XML is subset of SGML. Other examples of Markup languages are: HTML, MathML. Latex.

A markup language is just a set of rules, In SGML, for example, anything in angle brackets is considered markup. <...>

The makers of HTML used SGML to form a group of rules declaring what markup in HTML means. This set of rules is contained during a separate document called the HTML DTD (Document Type Definition). HTML DTD. for example, says that when you come across the in a document start a new paragraph.

MARKUP DELIMITERS

The part of XML: element tags are as follows: 

Consider the following example:

Symbol         -         Description

<                   -      Start tag open delimiter

</                 -      End tag open delimiter

foo                -     Element name

>                   -      Tag close delimiter

/>                 -      Empty tag close delimiter

It is worth remembering that, whereas HTML simply relies on recognizing pre-programmed tag XML is triggered by these specific parts of the element tag and the XML processors behavior and what it expects to see next are directly controlled by the name symbols.

EVOLUTION OF XML

XML (Extensible Markup Language) is a simple and flexible markup language. It improves on the HTML approach.

A huge amount of information is lost when data is converted into HTML. If this information can be preserved then it can be used to build a whole New World of more information. XML is all about preserving useful information on the web.

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The XML requires Internet Explorer 5.0 and above browsers to display is result. This browser on the XML built in parser. There are two types of parsers, one that only checks for the well-formed document, which is known as non-validating parser and the other is known as validating parser. The validating parser will check whether an XML document is well formed as well as the validation of DTDs. The latest browser by Netscape, i.e., Netscape 6.0, supports XML.

XML is a markup language that can run on any platform, operating system, or environment and is designed to provide developers with a mechanism to describe their content better.

It allows developers to write their own document type definition (DTD) that describe sets of tags and attributes that can be used to describe specific kind of content. DTDs are markup languages rulebooks that define what markup elements can be used to describe a document. If one wants to create one's own tags then we first need to define the tag in the DTD.

XML is a flexible framework. It enables to create one's own customized markup languages. All XML based languages will share the same look and feel. They will all share a common basic syntax. After this the developer is free to build his/her own diverse markup languages. 

Most of the XML-based markup languages are already a part of market today. For example, the Channel Definition Format (CDF). Electronic Commerce uses the Open Trading Protocol (OTP) and MML (Mathematical Markup Language) provides formatting for the mathematical equations.

XML has a definite advantage over HTML. HTML has a fixed set of predefined tags from which a page developer can choose and create his/her own page. On the other hand, XML does not define any particular set of tags. It provides a standardized framework with which one can define own tags and his/her needs.

RULES FOR XML

XML was developed since content specialists and designers realized that HTML is simply too limited scope to handle many tasks. It is not always simple to describe all content as paragraph, lists, tables and forms of HTML. The following points below list why XML is better than HTML.

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XML is a meta-language (ie can be used create new languages).

• Programs that process XML documents are easy to create and can be easily understood by all. However, to understand HTML one needs to have knowledge of its specific tags.

• The rules of an XML document are logical and simple. The XML syntax is easy to learn and utilize.

• The design of XML is formal. flexible and concise.

• XML checks for syntactical errors and the errors are mostly listed on the XML page. On the other hand. HTML lacks syntactical checking.

• The XML tag is case sensitive. For example, the tag <Myself> has a different effect than the tag <myself>. The beginning and ending tags must be the same.

• XML is particular on the aspect of the elements and their nested structure. HTML lacks structure, for instance the heading tags (H1 to H6) of HTML can be in any order. The browser is not particular about the order in which the heading tags are used.

XML files are documented in notepad and are saved with XML extension.