In this tutorial you will learn about XML, History, Introduction, Uses, XML Technology.
In 1970 IBM Introduced SGML (Standard Generalized Markup Language). SGML was developed out of the General Markup Language (GML), which was developed by IBM in the late 1960s.
SGML is a semantic and structural language for text documents but is very complicated. HTML is a subset of SGML.
In 1996 XML Working Group was formed under W3C .The World Wide Web Consortium (W3C) is an international consortium where Member organizations, a full-time staff, and the public work together to develop Web standards . W3C was created by Tim Berners-Lee in 1994 who also invented the World Wide Web in 1989. In 1998 W3C introduced XML 1.0.
XML (Extensible Markup Language) is a dialect of SGML. XML is not a programming language. Rather it is a set of rules that allow you to represent data in a structured manner. Since the rules are standard, the XML documents can be automatically generated and processed.
Its use can be gauged from its name itself –
- Markup – Is a collection of Tags
- XML Tags – Identify the content of data
- Extensible – User-defined tags
XML is a markup language much like HTML, but used for purposes different than what HTML is used for. It’s not a replacement for HTML. An XML document contains data that is tagged. XML documents are text documents. XML, like HTML uses tags and attributes (markup), but the tags in XML are used to describe data (e.g.,
XML was designed to describe data and is a cross-platform, software and hardware independent tool for transmitting or exchanging information. It is an open-standards-based technology which is both human and machine readable. XML are best suited for use in documents that have large amount of similarity.
XML has evolved from SGML (Standardized General Markup Language). The first version of XML
(version 1.0) was announced by W3C in 1998. Version 1.1 came out in early 2004.
In future Web development it is most likely that XML will be used to describe the data, while HTML will be used to format and display the same data. XML specification includes the syntax and grammar of XML documents as well as DTD.
XML is widely used for the following purposes
Storing data in a structured manner. ( Tree structure)
- Storing configuration information – typically data in an application which is not
stored in a database – Most server software have configuration files in XML formats
- XML documents can also be used as a mini data store. This data can be also used to present it on a variety of targets including browsers, print media, etc.
- Transmitting data between applications – Overcomes Problems in Client Server applications which are cross platform in nature Ex: A Windows program talking to a mainframe , Little and Big Endian problems, Data type size variations across platforms
When XML data is transferred across different systems, the data contained in an XML document can be read using a software entity called parser. Most of the popular databases (Oracle, MS SQL Server, Sybase, DB2, etc.) provide their own mechanisms to store and retrieve data as XML. Some of them also provide parsers to work with the XML documents programmatically.
XML is a key technology when it comes to Web Services. .NET uses XML extensively. It is used as a data format for everything – configuration files, metadata, RPC, object serialization.
XSD – XML Schema Definition
DTD - Document Type Definition.
XSL - Extensible Stylesheet Language.
The structured data is contained in an XML document, a text file with .xml as extension.
You can use CSS, like you use it for HTML, to provide style sheets for XML data display. For more advanced features, power, and flexibility for the presentations, you could use XSL (XML Style sheet Language) to build the style sheets. To enforce structural constraints and rules on the data contained in an XML document, you could code a DTD (Document Type Definition). Due to certain limitations that were inherent in DTDs, W3C came up with a newer specification to serve the same purpose as DTDs – the Schemas. The schemas are contained in a .xsd file, and DTDs in a .dtd file. XML Schema is an XML based alternative to DTD.