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An Introduction to XML

An Introduction to XML. Presented by Scott Nemec at the UniForum Chicago meeting on 7/25/2006. Definition(s). XML expands out to: eXtensible Markup Language A text based data document that can be read by a person using a text editor. What does XML do better?.

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An Introduction to XML

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  1. An Introduction to XML Presented by Scott Nemec at the UniForum Chicago meeting on 7/25/2006

  2. Definition(s) • XML expands out to: eXtensible Markup Language • A text based data document that can be read by a person using a text editor.

  3. What does XML do better? • XML fits between SGML (Standard Generalized Markup Language) and HTML (HyperText Markup Language) • SGML – very generalized markup language that is too complex for general usage • HTML – a markup language for display purposes that is not meant to have its definition modified. • XML is meant to let people define how its elements and attributes combine for each purpose it is used for.

  4. Why use XML? • Much more defined context and human-readable than other text like comma-delimited: Apple, 300, IL <sales> <company>Apple</company> <numberofIpods>300</numberofIpods> <state>IL</state> </sales>

  5. What makes up an XML document? • Elements • has a name, and contains a text value or another element(s) • An element can have more than one instance in a document • the element must show it being closed after the element value, if there is any value (ie. <element>a</element>, <element/>) • Example with fruit element: <fruit>apple</fruit> • Attributes • has a name, contains a text value, and is contained within an element. • it can only have one value per element instance in enclosing quotes • Example with ‘name’ attribute: <fruit name=‘apple’/> • Optional header • Provides information about the document, including links to definitions to be used for the document

  6. Well Formed? • ‘Well Formed’ means the xml document doesn’t have a syntax problem. • Every element has both an explicit start and an explicit or implicit end. That includes having matching ‘<‘ and ‘>’. • Attributes have a name, an ‘=‘ and single quotes (ie ‘ ) enclosing the value.

  7. Valid? • ‘Valid’ means the content of the format of the XML document matches a definition (either a schema or DTD) of what the content should be for the document. • An XML schema is the more modern definition which includes much more detail in what is can be defined. A schema file is defined as an XML document itself. • An XML DTD is the older definition specification. A DTD document is NOT defined as XML.

  8. Simple Examples • <?xml version="1.0" encoding="UTF-8"?> <element> <element2>A</element2> <element3>B</element3> <element3>C</element3> </element> • <?xml version="1.0" encoding="UTF-8“?> <q d=‘a’ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation=“filename.xsd"> <z>1</z> <z>2</z> </q>

  9. Advanced Topics • XSLT - Extensible Stylesheet Language Transformations • XPath - XML Path Language • XQuery - a language designed for processing XML data (ie XML databases) I recommend http://www.xml.com as a step for learning more about XML .

  10. References for further study • “A Really, Really, Really Good Introduction to XML” By Tom Myer http://www.sitepoint.com/article/really-good-introduction-xml • W3C Recommendation for XML definition 1.0 (third edition) http://www.w3.org/TR/REC-xml/ • XML from the Inside Out (O’Reilly) http://www.xml.com

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