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An Overview of Extensible Markup Language 8. An Overview of Extensible Markup Language (XML) 8.1 Introduction to XML XML is a new standard approved by the W3C (http://www.w3.org/XML). It roots go back to 1969, Charles Goldfarb, IBM researcher who in charge of the Generalized Markup Language (GML) team • Its predecessor: Standard Generalized Markup Language (SGML) • Another file format for storing information in hierarchical formats • Promises to increase both the efficiency and the flexibility of handling computerized information as needed in E-Commerce, for example you can specify a set new user defined tags: <PRICE> and </PRICE> that is unique to specific applications and is not limited by the tags available from HTML. • A XML document is saved with .xml as extension • It can describe both themselves and their content • An XML parser is required to interpret and display the document An XML-compliant application will process the following three files to display XML content: • The XML document o Containing document data o xml is used as the extension of the file name • A style sheet o Document display formatting rules for browsers o The file is saved with .css as the extension • Document Type Definition (DTD) o A rule file specifies how XML document elements, attributes, and other data o The file is saved with .dtd as the extension 8-1 An Overview of Extensible Markup Language 8.2 XML Resources XML Applications: • http://www.HL7.org (The Health Level Seven Organization Protocol) • http://www.ansi.org (ANSI Web site) • http://www-4.ibm.com/software/ad/features/xmi.html • http://www.w3.org/Math/ MathML (a XML-based Math Markup Language) • http://xml-cml.org (Chemical Markup Language) • http://www.venus.co.uk/omf/ChemML (a XML-based Chemestry Markup Language) • http://www.stars.com/Seminars/Language/OSD.html (Open Software Description) • http://www.ofx.net/ofx/default.asp (Open Financial Exchange) XML Resources: • http://www.ucc.ie/xml/ (The XML FAQ) • http://www.sil.org/sgml/xml.html (The SGML/XML Web Pages) • http://www.xml.com (XML.com) • http://www.xmlx.com (The XML Exchange) • http://www.w3.com (The World Wide Web Consortium) • http://xmlinfo.com (XML info) Development tools • Text editors (Notepad) • Word processors with XML capabilities (Microsoft Word, Corel WordPerferct) • Parsers (built-in browser) • Specialized XML development tools: o XML Pro (www.vervet.com) o Microsoft's XML Notepad (www.microsoft.com/xml/notepad/) o Visual XML (www.pierlou.com/visxml/) o XMLSpy (www.icon-is.com) 8-2 An Overview of Extensible Markup Language 8.3 XML Terminology • A XML document consists of one or more user defined elements • Each element has two tags: opening tag, and closing tag • Each element can have attributes • Empty element has no text appearing between two tags • Syntax: Start Tag:<ElementName AttributesName="AttributeValue"> End Tag: </ElementName> • Examples of elements: <PRICE Currency="Euro"> 26.02 </PRICE> <PICTURE> </PICTURE> <ARTICLE> <TITLE> </TITLE> <DATE> </DATE> <AUTHOR> <FIRSTNAME> </FIRSTNAME> <LASTNAME> </LASTNAME> </AUTHOR> <SUMMARY> </SUMMARY> <CONTENT> </CONTENT> </ARTICLE> 8-3