XML explained

In a nutshell, Extensible Markup Language is a markup specification language that allows programmers to design ways of describing information, usually for storage, transmission or processing by a program.

XML is considered a meta-language. That means it consists of data that describes other information, such as how it is formatted and how it can be exchanged between servers and clients via a network. By providing these features, XML makes it much simpler for programmers to develop applications that move information from system to system.

Whenever an application receives an XML file, it gets descriptions about how the data is structured. That way, a program can more easily determine how to process the data.

The applications for XML are broad. For example:

n The Federal Deposit Insurance Corp. has made XML the centerpiece of a Web publishing project planned for next year.

n Multiple agencies have created the XML-based FedStats.net — a Web site that provides a gateway to statistics from more than 100 federal agencies.

n The National Archives and Records Administration plans to convert records into XML-based documents as part of its Electronic Records Archive Program, so they can be read hundreds of years from now. n The Navy publishes XML-based engineering documents on the Web and uses XML-based electronic messaging.

The XML standard has some underlying components that make it work. XML tags define elements of the document such as a name or Social Security number. Tags draw on XML document type definitions, which describe the content and structure of a document. For example, an electronic payment might include customer name, address, account number, balance and bill number. Two systems with consistent DTDs can exchange files as easily as two PCs equipped with Microsoft Corp.'s Word.

XML schemas take DTDs a step further. They are more complete and coherent documents necessary for more advanced data exchange efforts. They provide a means for defining the structure, content and semantics of XML documents.

XML style sheets tell applications how to present information to different devices. One style sheet may outline how to present a report for a user to view with a Web browser, while a second could illustrate how to send the report to a user with a wireless phone.

XML components enable programmers to spend less time worrying about data exchanges and more time on application functionality.

XML is new, but not that new. XML has been a World Wide Web Consortium standard since 1998, but it is based on Standard Generalized Markup Language, which was developed in the early 1980s.

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