XML Extensible Markup Language

1
XML Extensible Markup Language

• protocols ?

2
Markup

• 1. Stylistic how a document is presented
• ltBgtltUgtltIgt
• 2. Structural how the document is to be
  structured
• ltHRgtltDIVgt
• 3. Semantic tell about the content of data.
• ltHEADgtltTITLEgt

3
Some History

• SGML (Standard Generalized Markup Language)
• ISO Standard, 1986, for data storage exchange
• Metalanguage for defining languages (through
  DTDs)
• A famous SGML language HTML!!
• Separation of content and display
• Used in U.S. gvt. contractors, large
  manufacturing companies, technical info.
  Publishers,...
• SGML reference is 600 pages long
• XML (eXtensible Markup Language)
• W3C (World Wide Web Consortium) --
  http//www.w3.org/XML/ recommendation in 1998
• Simple subset (80/20 rule) of SGML ASCII of
  the Web, Semantic Web
• XML specification is 26 pages long

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SGML XML HTML

• SGML provides arbitrary structure. Full SGML
  systems solve large, complex problems that
  justify their expense.
• XML is defined as an application profile of SGML,
  or roughly speaking, a restricted form of SGML.
  XML specifies neither semantics nor a tag set.
  XML provides a facility to define tags and the
  structural relationships between them.
• In HTML, both the tag semantics and the tag set
  are fixed.

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The main difference between XML and HTML

• XML was designed to carry data.
• XML is not a replacement for HTML.XML and HTML
  were designed with different goals
• XML was designed to describe data and to focus on
  what data is.HTML was designed to display data
  and to focus on how data looks.
• HTML is about displaying information, while XML
  is about describing information

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XML is ...

• ... an eXtensible Markup Language
• ... HTML ? presentation tags your-own-tags
• ... a meta-language for defining other languages
• ... a semistructured data model
• ... not a data model but just an exchange syntax
• ... many good (and some bad) Computer Science
  ideas reinvented (but now for the masses!)
• ... good old constant change

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XML as a Self-Describing Data Exchange Format

• can be easily understood by our friend (...
  even using CP/M edlin)
• can be parsed easily
• contains its own structure (parse tree) in the
  data
• gt allows the application programmer to
  rediscover schema and content/semantics (to
  which extent???)
• may include an explicit schema description
  (e.g., DTD)
• gt meta-language definition of a language w.r.t.
  which it is valid
• allows separation of marked-up content from
  presentation (gtstyle sheets)
• many tools (and many more to come -- (re)use
  code) parsers, validators, query languages,
  storage,
• standards (good for interoperation, integration,
  etc)
• gt generic standards (XML, DTDs, XML Schema,
  XPath,...)
• gt community/industry standards (specific markup
  languages)

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10 Commandmends of XML

• XML shall be straightforwardly usable over the
  Internet.
• XML shall support a wide variety of applications.
• XML shall be compatible with SGML.
• It shall be easy to write programs which process
  XML documents.
• The number of optional features in XML is to be
  kept to the absolute minimum, ideally zero.
• XML documents should be human-legible and
  reasonably clear.
• The XML design should be prepared quickly.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance.

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• The XML declaration
• The Document Type Declaration
• The element data
• The attribute data
• The character data or XML content

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XML Declaration

• lt?xml
• version1.0
• standalonexxx yes/no
• encodexxx big-5, US-ASCII
• UTF-8

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• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltnotegt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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Internet Explorer 6

• Internet Explorer 6 has full XML support,
  including Namespaces, Style sheets in CSS, and
  XSLT 1.0.
• The built-in XML Parser 3.0 in Internet Explorer
  6.0 and Windows XP is based on both the W3C XSLT
  1.0 and the W3C XPath 1.0 Recommendations

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• Internet Explorer has the following XML support
• Viewing of XML documents
• Full support for W3C DTD standards
• XML embedded in HTML as Data Islands
• Binding XML data to HTML elements
• Transforming and displaying XML with XSL
• Displaying XML with CSS
• Access to the XML DOM
• Internet Explorer also has support for Behaviors
• Behaviors is a Microsoft-only technology  
• Behaviors can separate scripts from an HTML page.
  
• Behaviors can store XML data on the client's
  disk.

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Root Element

• ltnotegt
• Child elements of root element
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt ltheadinggtReminderlt/headinggt
  ltbodygtDon't forget me thisweekend!lt/bodygt
• All XML documents must have a root element

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Element Naming

• Names can contain letters, numbers, and other
  characters
• Names must not start with a number or punctuation
  character
• Names must not start with the letters xml (or
  XML, or Xml, etc)
• Names cannot contain spaces

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Comments in XML

• The syntax for writing comments in XML is similar
  to that of HTML.
• lt!-- This is a comment --gt

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attributes

• ltbookgt lttitlegtMy First XMLlt/titlegt ltprod
  id"33-657" media"paper"gtlt/prodgt
• lt/bookgt
• the prod element has attributes. The attribute
  named id has the value "33-657". The attribute
  named media has the value "paper". 
• Attribute values must always be quoted

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• ltperson sex"female"gt ltfirstnamegtAnnalt/firstnamegt
  ltlastnamegtSmithlt/lastnamegt
• lt/persongt
• ltpersongt
• ltsexgtfemalelt/sexgt ltfirstnamegtAnnalt/firstnamegt
  ltlastnamegtSmithlt/lastnamegt
• lt/persongt

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XML Validation

• XML with correct syntax is Well Formed XML.
• Errors in XML documents will stop the XML program

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All XML elements must have a closing tag.

• With XML, it is illegal to omit the closing tag.
• ltpgtThis is a paragraph
• ltpgtThis is a paragraphlt/pgt

21
All XML elements must be properly nested

• Improper nesting of tags makes no sense to XML.
• ltbgtltigtThis text is bold and italiclt/bgtlt/igt
• ltbgtltigtThis text is bold and italiclt/igtlt/bgt

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XML tags are case sensitive

• ltMessagegtThis is incorrectlt/messagegt
• ltmessagegtThis is correctlt/messagegt

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Escape Characters

• Illegal XML characters have to be replaced by
  entity references
• ltmessagegtif salary lt 1000 thenlt/messagegt
• ltmessagegtif salary lt 1000 thenlt/messagegt

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• There are 5 predefined entity references in XML
• ltlt less than
• gtgt greater than
• amp ampersand 
• apos apostrophe
• quot quotation mark
• Note Only the characters "lt" and "" are
  strictly illegal in XML. Apostrophes, quotation
  marks and greater than signs are legal, but it is
  a good habit to replace them.

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CDATA (Character data)

• Everything inside a CDATA section is ignored by
  the XML processor
• Contents will pass to application
• A CDATA section starts with "lt!CDATA" and ends
  with "gt"
• A CDATA section cannot contain the string "gt",
  therefore, nested CDATA sections are not allowed.
• Also make sure there are no spaces or line breaks
  inside the "gt" string.

26

• ltscriptgt
• lt!CDATA
• function matchwo(a,b)
• if (a lt b a lt 0)
• then return 1
• else return 0
• gt
• lt/scriptgt