XML (Extensible Markup Language)

XML (Extensible Markup Language) is a flexible way to create common information formats and share both the format and the data on the World Wide Web, intranets, and elsewhere. For example, computer makers might agree on a standard or common way to describe the information about a computer product (processor speed, memory size, and so forth) and then describe the product information format with XML. Such a standard way of describing data would enable a user to send an intelligent agent (a program) to each computer maker's Web site, gather data, and then make a valid comparison. XML can be used by any individual or group of individuals or companies that wants to share information in a consistent way.

XML, a formal recommendation from the World Wide Web Consortium (W3C), is similar to the language of today's Web pages, the Hypertext Markup Language (HTML). Both XML and HTML contain markup symbols to describe the contents of a page or file. HTML, however, describes the content of a Web page (mainly text and graphic images) only in terms of how it is to be displayed and interacted with. For example, the letter "p" placed within markup tags starts a new paragraph. XML describes the content in terms of what data is being described. For example, the word "phonenum" placed within markup tags could indicate that the data that followed was a phone number. This means that an XML file can be processed purely as data by a program or it can be stored with similar data on another computer or, like an HTML file, that it can be displayed. For example, depending on how the application in the receiving computer wanted to handle the phone number, it could be stored, displayed, or dialed.

XML is "extensible" because, unlike HTML, the markup symbols are unlimited and self-defining. XML is actually a simpler and easier-to-use subset of the Standard Generalized Markup Language (SGML), the standard for how to create a document structure. It is expected that HTML and XML will be used together in many Web applications. XML markup, for example, may appear within an HTML page.

Early applications of XML include Microsoft's Channel Definition Format (CDF), which describes a channel, a portion of a Web site that has been downloaded to your hard disk and is then is updated periodically as information changes. A specific CDF file contains data that specifies an initial Web page and how frequently it is updated. Another early application is ChartWare, which uses XML as a way to describe medical charts so that they can be shared by doctors.Applications related to banking, e-commerce ordering, personal preference profiles, purchase orders, litigation documents, part lists, and many others are anticipated.



Getting started with XML
To explore how the Extensible Markup Language is used in the enterprise, here are some additional resources:
What’s up with XML 2.0? Ed Tittel discusses the new version of XML 2.0 and the characteristics that differentiate it from the original XML.
XML to the rescue: Data governance in SOA: Many SOA installations are running into performance issues because they lack proper data governance. Ed Tittel explains how to use XML to create a data services layer.
XML integration with SQL Server 2005 chapter download: Discover how XML in SQL Server 2005 offers a new level of unified storage support for relational database engine. Get new XML features in SQL Server 2005.
XML data type in SQL Server 2005 vs. VARCHAR (MAX): Learn performance impacts of the XML data type and VARCHAR (MAX) data type in SQL Server 2005. Here are storage, I/O and CPU results of XML in SQL Server.
T-SQL commands vs. XML AUTO in SQL Server: XML Auto and T-SQL commands in SQL Server 2005 use different amounts of resources. Learn performance implications when comparing XML Auto with T-SQL.

Contributor(s): Tamas E. Doszkocs, Gerhard Hill, Fredrik Lindgren, and Neil Yashinsky
This was last updated in May 2007
Posted by: Margaret Rouse

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