An%20Introduction%20to%20XML

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
• ltsalesgt
• ltcompanygtApplelt/companygt
• ltnumberofIpodsgt300lt/numberofIpodsgt
• ltstategtILlt/stategt
• lt/salesgt

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.
  ltelementgtalt/elementgt, ltelement/gt)
• Example with fruit element ltfruitgtapplelt/fruitgt
• 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 ltfruit
  nameapple/gt
• 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 doesnt have
  a syntax problem.
• Every element has both an explicit start and an
  explicit or implicit end. That includes having
  matching lt and gt.
• 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

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltelementgt
• ltelement2gtAlt/element2gt
• ltelement3gtBlt/element3gt
• ltelement3gtClt/element3gt
• lt/elementgt
• lt?xml version"1.0" encoding"UTF-8?gt
• ltq da xmlnsxsi"http//www.w3.org/2001/XMLSch
  ema-instance" xsinoNamespaceSchemaLocationfilen
  ame.xsd"gt
• ltzgt1lt/zgt
• ltzgt2lt/zgt
• lt/qgt

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-intr
  oduction-xml
• W3C Recommendation for XML definition 1.0 (third
  edition)
• http//www.w3.org/TR/REC-xml/
• XML from the Inside Out (OReilly)
• http//www.xml.com