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XML Tutorial - Index
XML Tutorial - Introduction to XML
XML Tutorial - How XML interact with data?
XML Tutorial - How to write first XML document
XML Tutorial - What are XML Elements and Attributes?
XML Tutorial - What is XML Schema and DTD?
XML Tutorial - Which Browser support XML?
XML Tutorial - XML and Styles
XML Tutorial - Embedding XML in HTML
XML Tutorial - Working with XML Parser
XML Tutorial - Working with CDATA
     

 
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  Home > Courses, Tutorials & eBooks > XML Tutorial > Introduction to XML
 

XML Tutorial - Introduction to XML

 
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Overview
 
In this chapter you will learn :
  • What does XML stands for?
  • Where XML is used?
  • What are the benefits of using XML?
  • Requirements for learning.
  • How is it different from HTML?

XML

XML stands for eXtensible Mark up Language. XML was developed by the W3C (World Wide Web Consortium) between 1996 and 1998 to provide a universal format for describing structured documents and data. The XML is a subset of SGML (Standard Generalized Markup Language), that was designed to comply with the basic need of making data storage independent of any one software package. SGML is a meta language, i.e., a language used for describing other mark up languages.
                The SGML existed a long before XML, but never given much acceptance. Basically, SGML is a very complicated language, when used extensively for web. It requires too much of an investment in time, tools and training.
HTML, too, cited complaints like :

  • HTML lacks syntactic checking. There is no way to validate HTML code.

  • HTML lacks internal structure.

  • HTML has not been standardized as with SGML.

  • HTML cannot handle data interchange, i.e., HTML tags does not identify the information contained in the document. 

  • There is no concept of reusing code. HTML cannot reuse its code.

  • HTML is not extensible.

XML uses the features of SGML. XML is designed in such a way that it is inter-practicable with both SGML and HTML. Also it provides ease of implementation with both. So, XML takes the best of SGML and combines it with some of the best features of HTML. Various features of XML are :

  • XML is an abbreviation for eXtensible Mark up Language.

  • XML is a language developed for the web which is different to any other type of scripting or programming language available before it.

  • XML is a framework for defining mark up languages.

  • XML is known as a simplified subset of the SGML, the goal of which is to enable generic SGML to be served, received and processed on the web.

  • XML is a W3C recommendation. It is recommended by a group of vendors, including Microsoft and Sun, called the World Wide Web Consortium (W3C).

  • XML has no fixed collection of mark up tags. You can define your own tags.

  • XML allows data to be self-describing, i.e., it is designed to describe data and to focus on what data is rather than specifying how to display it.

  • XML is hierarchical in nature which means a nested tag pair cannot overlap with another tag.

  • In XML, every opening tag must have a corresponding closing tag.

  • XML can be categorized as both a meta-language and a markup language

Benefits of XML

  • XML is a simple language as information contained in an XML program can be read and can be easily processed by any computer.

  • As XML is W3C standard, various software companies have openly accepted and implemented it in their operations.
  • XML can handle high volumes of information especially over the internet and World Wide Web.

  • XML can be used with existing web protocols (such as HTTP and MIME) and mechanisms (such as URL's ), and it does not impose any additional requirements.

  • XML operates on data orientation than readability by humans. Although being humanly readable is one of XML's design goals.

  • There are no fixed tags for XML. Any user can add his own set of tags. XML tags does not describe presentation but meaning.

  • XML can support data written in some other language too.

  • XML data can be sent to some cell phones, which is then formatted by the specification of the cell phone software designer to display text, images and even play sounds.

Requirements for learning XML

This tutorial is intended to provide an introduction to what XML is and how it can be used. Prerequisites include only some basic knowledge of World Wide Web (WWW) services and HTML coding. No previous experience with XML is necessary.

How XML is different from HTML?

XML and HTML are identical in many respects. Both are derived from SGML, both have start tag and end tag and both have elements and attributes associated with the tags. So they appear very similar. However, XML is not like HTML. Various differences encountered are :

  • The key concept to remember is that XML was designed to describe data and to focus on what the data actually is. HTML, on the other hand, was designed to display content and to focus on how the content looks. In other words, HTML is about displaying information, XML is about describing information.

  • There are predefined set of HTML tags designed for we pages and the tag semantics are fixed in the HTML standard whereas XML can have user-defined tags. The tags in XML are not predefined and neither do their semantics.

  • In XML, every opening tag must have a corresponding closing tag. However, in HTML pairing is optional for certain tags, and only the opening tag is required.


    For example, browsers will accept the following HTML code :
                                      <P>The paragraph contains opening tag only.
                                      <P>This paragraph, too, has opening tag only.
    XML, however, has been designed to eliminate this possibility with the rigid rule that every opening tag must have a matching closing tag.

  • In XML, a nested tag pair cannot overlap with another tag whereas HTML allow tags to appear without satisfying the rules of proper nesting.

    For example,
    Following lines of HTML code contain tags that aren't properly nested :
                         <STRIKE><BOLD>In this example, code is bold.</BOLD></STRIKE>
                         <SUP><SMALL>This is second example.</SUP></SMALL>
    These lines of code, however, would be illegal in XML. In XML, the closing tag must match the last-used opening tag.
  • HTML is not extensible whereas XML adds extensibility. XML's powerful linking mechanisms allow you to link to material without requiring the target to be physically present in the object.


  • HTML is not international, where as, XML is based on Unicode. Unicode enables XML to handle not just Western-accented characters, but also Asian languages.
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Summary
 

In this chapter you have learnt:

  • About evolution of XML.
  • Difference between HTML and XML.
  • Benefits of using XML.
  • Prerequisites of learning XML.

 

 
 
Review Questions
 

Fill in the Blanks

  1. XML stands for --------- Mark up Language.
  2. XML is a subset of -------.
  3. In XML, every ------ tag must have a corresponding ------ tag.

Solutions

  1. eXtensible
  2. SGML
  3. opening, closing

State whether True or False

  1. SGML is a meta-language.
  2. HTML supports reusability of code.
  3. XML has fixed number of tags.

 

Solutions
  1. True
  2. False
  3. False

 

 
 
What's Next

The next chapter will acquaint you with the basic concept of how XML interacts with data. The chapter will further elucidate how XML share, exchange, store and carry data.

                 Hop over to the next chapter to get XML interaction with data close-up.

 
   
 
 
     
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