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EXtensible Markup Language (XML)

1. Introduction: EXtensible Markup Language (XML) is a simple, very flexible text format derived from Standard Generalized Markup Language (SGML) (ISO 8879). XML is a markup language that defines a set of rules for encoding documents in a format which is both human-readable and machine-readable. There are two current versions of XML. The first (XML 1.0) was initially defined in 1998. The second (XML 1.1) was initially published on February 4, 2004. XML became a W3C Recommendation on February 10, 1998. eXtensible HyperText Markup Language (XHTML) is a reformulation of HTML in XML syntax. While very similar in many respects, it has a few key differences. eXtensible HyperText Markup Language (XHTML) is a family of XML markup languages that mirror or extend versions of the widely used Hypertext Markup Language (HTML).
XML was designed to describe data, with focus on what data is, whereas HTML was designed to display data, with focus on how data looks.
The tags used in HTML are predefined i.e. HTML documents can only use tags defined in the HTML standard like <p>, <h1>, etc.. Whereas, eXtensible Markup Language (XML) grew out of a desire to be able to use more than just the fixed vocabulary of HTML on the web. XML allows the author to define his/her own tags and his/her own document structure. So, it can be said that the XML has user-defined tag and html is pre-defined tags.
XML always needs close tags, and has a special syntax for tags that don’t need a close tag. However, in HTML, some tags, such as <img /> are always assumed to be empty and close themselves. Others, like <p> may close implicitly based on other content. And others, like <div> always need to have a close tag. In XML (including XHTML), any tag can be made self-closing by putting a slash before the code angle bracket, for example <img src="badan-barman.jpg"/>. In HTML that would just be <img src=" badan-barman.jpg ">
XML is a meta-markup language, like SGML, but one that simplifies many aspects to make it easier to make a generic parser. A meta language is a language that provides a syntax mechanism for creating other languages without constraining expression through a predefined grammar.

2. Usefulness and Problems of XML: XML-based formats have become the default for many office-productivity tools, including Microsoft Office (Office Open XML), and LibreOffice (OpenDocument), and Apple’s iWork. Other common uses of XML are
a) XML Separates Data from HTML: With XML, data can be stored in separate XML files. This way you can concentrate on using HTML/CSS for display and layout, and be sure that changes in the underlying data will not require any changes to the HTML.
b) XML Simplifies Data Sharing: In XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data.
c) XML Makes Your Data More Available: With XML, your data can be available to all kinds of reading machines i.e. handheld tablet, voice machines, news feeds, computer, etc. and make it more available for blind people, or people with other disabilities. XML allow for communication between applications.
The problem with XML is that it is too complex in comparison to HTML and so hard to use by non expert.

3. Basic Syntax of XML: XML language has no predefined tags. With XML you invent your own tags. Further, XML tags are case sensitive. In XML, it is illegal to omit the closing tag i.e. all elements must have a closing tag. In XML, all elements must be properly nested within each other. <b><i>This text is bold and italic</i></b>, in this example, Properly nested simply means that since the <i> element is opened inside the <b> element, it must be closed inside the <b> element. XML documents may begin by declaring some information about themselves.
Example: <?xml version="1.0" encoding="UTF-8"?> .
Comments start with "<!--" and end with "-->" in XML.

4. How to Use XML: In the following example the first line is the XML declaration. It defines the XML version (1.0). The next line describes the root element of the document (like saying: this document is a note). The next 4 lines describe 4 child elements of the root (to, from, heading, and body) and finally the last line defines the end of the root element.

<?xml version="1.0" encoding="UTF-8"?>
<to>Professor Narendra Lahkar</to>
<from>Dr. Badan Barman</from>
<heading>LIS Links Website</heading>
<body>Sir, Kindly take the trouble to inform the students about the LIS Links website</body>

5. Conclusion: XML was compiled by a working group of eleven members, supported by a (roughly) 150-member Interest Group. The XML Working Group never met face-to-face; the design was accomplished using a combination of Email and weekly teleconferences. The major design decisions were reached in a short burst of intense work between August and November 1996, when the first Working Draft of an XML specification was published. Further design work continued through 1997, and XML 1.0 became a W3C Recommendation on February 10, 1998.

How to Cite this Article?
APA Citation, 7th Ed.:  Barman, B. (2020). A comprehensive book on Library and Information Science. New Publications.
Chicago 16th Ed.:  Barman, Badan. A Comprehensive Book on Library and Information Science. Guwahati: New Publications, 2020.
MLA Citation 8th Ed:  Barman, Badan. A Comprehensive Book on Library and Information Science. New Publications, 2020.

Badan BarmanBadan Barman at present working as an Assistant Professor in the Department of Library and Information Science, Gauhati University, Guwahati-781014, Assam, India. He is the creator of the LIS Links ( - India’s most popular social networking website for Library and Information Science professionals. He also created the UGC NET Guide ( and LIS Study ( website.

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