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Basic XML Concepts
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  1. Basic XML Concepts Web Programming Maymester 2004

  2. XML fundamental concepts • XML is not a language, but a structure for defining application-specific mini-languages • Tags, elements and attributes • Tag names can be ANYTHING (depends on application

  3. Example XML document

  4. XML/HTML entities • Some symbols cannot appear in document content because they confuse parsing • Entities represent these symbols

  5. Well-Formed XML document • Every tag has a matching closing tag • Tags are properly nested • You can have an empty element, which is its own matching close tag • <danger voltage=“480” /> • All attribute values appear in quotes

  6. Valid XML document • A valid document must be well-formed • In addition, the document conforms to a language definition • The language definition specifies possible tags, their contents, and their attributes • Two types of language definitions: • Document Type Definition (DTD) • XML Schema

  7. Document Type Definition • Example: a letter contains a source and destination address, a salutation, one or more paragraphs, and a closing

  8. DTD Attribute Definitions • REQUIRED: must always appear • IMPLIED: optional • FIXED: required, and always has same value

  9. DTD Data Types & Quantifiers • #PCDATA =“parsed character data”, can contain no XML markup chars • Use entities to replace markup chars • “X+” means one or more instances of X • “X*” means zero or more instances of X • “X?” means zero or one instances of X

  10. Where to put DTDs • Can be embedded in the DOCTYPE declaration, as in previous example • SYSTEM DTD refers to a file on the same machine: • PUBLIC DTD gives a URL to the DTD:

  11. XML Schema • Document definition file is also an XML document, unlike DTD • Gives much tighter control over contents of XML document • See http://www.w3.org/TR/2000/CR-xmlschema-0-20001024/ for details

  12. XHTML • HTML that conforms to XML format • Stricter grammar rules than HTML 4.01 Strict • All tag names in lower case • V

  13. Acknowledgements Examples taken from Sun J2EE tutorial, http://java.sun.com/webservices/docs/1.3/tutorial/doc/IntroXML.html