XML

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XML

• Introduction to XML
• Document Type Definition (DTD)
• XML Parser
• Example CGI Gateway to XML Middleware

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1. Introduction to XML

• CGI Middleware can perform sophisticated
  processes on several data sources that itself
  becomes a data source. XML provides an industry
  standard way of describing data from different
  data sources. CGI programs that speak XML will be
  able to deliver to and retrieve data from any
  XML-compliant Perl script or Java applet.

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Introduction to XML

• HTML was deigned for the data presentation
  language (display the content for human to read),
  it lacks of the data description capability
  (cant interpret the data for machine to
  understand.)
• Example ltBgtWhitelt/Bgt
• XML was designed to make up many of HTMLs
  limitations. It is a data description language
  that is useful as a mechanism for transporting
  data from program to program on different
  platforms.
• Example ltLastNamegtWhitelt/LastNamegt

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XML Features

• New tags and tag hierarchies can be defined to
  represent data specific to your application. For
  instance, a quiz can contain ltQUESTIONgt and
  ltANSWERgt tags.
• Document type definitions can be defined for data
  validation. You can require, for instance, that
  every ltQUESTIONgt be associated with exactly one
  ltANSWERgt.
• Data transport is Unicode-compliant, which is
  important for non-ASCII character sets.
• Data is provided in a way that makes it easily
  transportable via HTTP.
• Syntax is simple, allowing parsers to be simple.

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Example

• lt?xml version"1.0"?gt
• lt!DOCTYPE quiz SYSTEM "quiz.dtd"gt
• ltQUIZgt
• ltQUESTION TYPE"Multiple"gt
• ltASKgt All of the following players won the
  regular season MVP and playoff MVP in the same
  year, except for lt/ASKgt
• ltCHOICE VALUE"A" TEXT"Larry Bird"/gt
• ltCHOICE VALUE"B" TEXT"Jerry West"/gt
• ltCHOICE VALUE"C" TEXT"Earvin Magic
  Johnson"/gt ltCHOICE VALUE"D" TEXT"Hakeem
  Olajuwon"/gt
• ltCHOICE VALUE"E" TEXT"Michael
  Jordan"/gt
• ltANSWERgtBlt/ANSWERgt
• ltRESPONSE VALUE"B"gt West was awesome, but
  they did not have a playoff MVP in his day.
  lt/RESPONSEgt
• ltRESPONSE STATUS"WRONG"gt How could you
  choose Bird, Magic, Michael, or Hakeem?
  lt/RESPONSEgt
• lt/QUESTIONgt

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Example (Cont.)

• ltQUESTION TYPE"Text"gt
• ltASKgt Who is the only NBA player to get a
  triple-double by halftime? lt/ASKgt
• ltANSWERgtLarry Birdlt/ANSWERgt
• ltRESPONSE VALUE"Larry Bird"gt You got it! He
  was quite awesome! lt/RESPONSEgt
• ltRESPONSE VALUE"Magic Johnson"gt Sorry. Magic
  was just as awesome as Larry, but he never got a
  triple-double by halftime. lt/RESPONSEgt
• ltRESPONSE STATUS"WRONG"gt I guess you are not a
  Celtics Fan. lt/RESPONSEgt
• lt/QUESTIONgt
• lt/QUIZgt

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XML Document

• All XML documents must present the data with at
  least one root structure surrounding the whole
  document.
• XML accept all HTML tags, but it requires closed
  tag for all the tags.
• XML parser converts the XML document into
  standard HTML. It uses the a dtd file to define
  how the XML document is structured and what the
  tags mean in relation to another
• Example quiz.dtd (next page)
• XSL (Extensible Style sheet Language) defines the
  standard stylesheet language for XML. It takes
  the original document tree and creates a new one
  based on the instructions that the developer
  provide.

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2. Document Type Definition quiz.dtd

• lt?xml version-"1.0"gt
• lt!ELEMENT QUIZ (QUESTION)gt
• lt!ELEMENT QUESTION (ASK,CHOICE,ANSWER,RESPONSE
  )gt
• lt!ATTLIST QUESTION
• TYPE CDATA REQUIREDgt
• lt!ELEMENT ASK (PCDATA)gt
• lt!ELEMENT CHOICE EMPTYgt
• lt!ATTLIST CHOICE
• VALUE CDATA REQUIRED
• TEXT CDATA REQUIREDgt
• lt!ELEMENT ANSWER (PCDATA)gt
• lt!ELEMENT RESPONSE (PCDATA)gt
• lt!ATTLIST RESPONSE
• VALUE CDATA
• STATUS CDATAgt

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DTD

• The DTD file is optional. XML document with the
  DTD file is called valid XML document. (without
  DTD is called well-formed document)
• The lt!ELEMENTgt tags describe the actual tags that
  are valid in the XML document. The parentheses
  after the name of the element show what tags it
  can contain. The symbol is a quantity
  identifier. It follows the same basic rules as
  regular expression matching.
• After each element is defined, its attributes
  need to be laid out.
• Example Questions have a type attribute that
  takes a string of character data. Furthermore,
  the REQUIRED keyword indicates that this data is
  required in the XML document.

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3. XML Parser

• XML parsers parse data in two different ways.
• To have the XML parser take the entire document
  and simply return a tree of objects that
  represents the XML document hierarchy. Perl
  supports this concept via the XMLGrove module.
• (Similar with Java DOM (Document Object Model)
  API)
• To parse XML documents is using a SAX (Simple API
  for XML) style of parser. This type of parser is
  event-based and is the one that XMLParser is
  based on. CGI Perl XMLParser is an interface to
  a library written in C called expat.
• (Similar with Java SAX API)

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4. Example CGI Gateway to XML Middleware

• CGI gateway script parsing the XML from the
  Netscape Whats Related XML middleware server.

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Example CGI Gateway to XML Middleware

• User provides a URL whats_related.html
• whats_related.cgi
• get(http//www-rl.netscape.com/wtgn?, url)
  returns the directly related URL in a XML data
  document (without DTD).
• XMLParser parse XML data document into a HTML
  document.
• sub get_whats_related_to_whats_related will
  iterate through the directly related urls to get
  next level related urls.