What Is XML?

photo of John Michael Pierobon By: John Michael Pierobon

The next generation of Web sites will be written in XML. XML stands for eXtensible Markup Language. XML is the universal format for structured documents and data on the Web.

Web sites are developed today using the HyperText Markup Language (HTML), which defines, or marks up, the presentation of a page by embedding tags into the page. These tags start with a "<" and end with a ">". Tags define sources and destinations of hyperlinks, how text is displayed, where images are inserted on the page, etc.

While Web pages can be very sophisticated, HTML is limited to how the information is presented. XML goes beyond its predecesor by describing the content and the semantics of data in addition to the presentation of data. XML is really a meta language for describing markup languages. It provides a facility to define tags and the structural relationships between them, analogous to defining the words (tags) and the grammar (structural relationships) of a language.

XML has no predefined set of tags, therefore there are no preconceived semantics. All of the semantics of an XML document will either be defined by the applications that process them or by style sheets.

Style sheets describe how documents are presented on screens, in print, or perhaps even how they are pronounced. By attaching style sheets to structured documents on the Web, authors and viewers can influence the presentation of documents without adding new tags.

Since XML-formatted data can be directly manipulated, queried, and shared by applications and tools that understand XML, large computer companies such as IBM and Microsoft are developing efficient ways to tightly integrate XML with Relational DataBase Management Systems (RDBMS). This is particularly interesting because information which is important to us, such as payroll records, bank and credit card accounts, medical records, tax rolls, inventory levels, etc., are all stored on computers in tables which comprise RDBMS.

XML has the opportunity to be the primary enabler of the next generation of Web applications, and to enhance the performance of today's Web applications. For example, a search engine that understands structured documents like XML can significantly improve the effectiveness of text searches. How many times have you gone to a search engine and have it return results that did not yield the exact information you were looking for?

Today, when you switch doctors or credit card companies, medical records or credit information has to be transferred from one RDBMS to another. Often this is done manually because the RDBMS are incompatible. Many times this incompatibility is due to semantics.

Because XML is a meta language, it also has the ability to describe metadata. Metadata is data about data. Any tool that requires metadata can use XML to exchange metadata. This leads to interoperability between different RDBMS because two or more RDBMS will now be able to understand the meaning or the context of the data that is being exchanged.

With XML, vendors and suppliers will be able to exchange data more efficiently, which will eventually lead to lower costs, better service, and higher quality. The most obvious benefit of XML will be ease of use because XML will use that universal tool known as the browser.

John Michael Pierobon is an Internet consultant based in Fort Lauderdale.
John Michael may be reached by sending electronic mail to pierobon@pierobon.org

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