What is XML?

 

HTML is still considered to be most favorite markup language and millions of web pages have been written using HTML. Now people have started realizing the inherent limitations with HTML and a swing towards XML is being felt. Following are some of the limitations of HTML which have been reported.

• HTML lacks syntactic checking i.e. validation of HTML code.
• HTML is not content aware. 
• HTML is not suitable for data interchange.
• HTML lacks a robust linking mechanism.
• HTML is not extensible.
• Above all, HTML defines and uses its fixed set of tags. XML solve this problem with limited flexibility.

XML is derived from SGML. SGML(Standard Generalized markup language) is a meta language or a language for describing for markup languages. HTML is one such markup language and is therefore called an SGML application. XML uses the features of SGML that is needs and tries to incorporate the lessons learned from HTML. XML is a set of rules for defining the semantic tags that breaks the document into parts. The tags in XML may be used in such a way that XML makes easy various web development tasks which were quite painful in doing with HTML. Various features of XML are listed below. These features make XML a programmers choice for web development.

• XML can be use existing web protocols(such as HTTP and MIME) and mechanisms(such as URLs) and it does not impose any additional requirements.
• XML supports a wide variety of applications. It is difficult to support a lot of applications with just HTML; hence, the growth of scripting language.
• It is easy to write programs that process XML documents.
• The number of optional features in XML has been kept to an absolute minimum.
• XML documents are reasonably clear to the lay person.
• The design of XML is formal and concise.
• XML documents are easy to create.

 XML is commonly called a subject of SGML but actually it is an application profile of SGML whereas HTML uses SGML and is an application of SGML, XML is just SGML on a similar scale. From HTML, XML inherits the use of web address(URLs) to point to other objects.