XML

1
XML

• CS 105

2
What is XML?

• XML stands for Extensible Markup Language.
• XML is a markup language like HTML.
• XML was designed to describe data.
• You must define your own tags.

3
An XML Example

• ltnotegt
• lttogtJohnlt/togt
• ltfromgtMerrylt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDont forget to pick up the boxlt/bodygt
• lt/notegt

4
Why XML?

• There is a huge number of websites on the web and
  each website posts tunes of web pages. Also the
  number of web sites increases day by day.
• It is getting harder to find the information we
  are looking for.

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Why XML?

• We need search engines to locate the information
  that we are looking for.
• Most of the WWW documents are in HTML.
• Search engines can bring you tons of pages.
• Note that we humans are smart. Most of the times
  we can realize the content of a webpage by
  reading it. But computer programs are not and
  search engine is a computer program.

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XML is the solution.

• HTML describes how to display a page.
• But it does nothing to describe the contents of a
  page.
• We need a language to convey the content of a web
  page.
• XML is the solution.

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XML

• XML indicates
• What information is contained within a webpage.
• Where that information is on the page.

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XML and HTML

• XML is not a replacement for HTML
• XML was designed to describe data in a format
  that you want and to focus on what data is.
• HTML was designed to display data in a format
  that you prefer.
• HTML is about displaying information, while XML
  is about describing information

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XML and HTML

• XML and HTML complement each other.
• XML describes the data.
• HTML displays the data.

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eXtensible Markup Language

• eXtensible
• Markup
• Language
• XML is supported by many platforms and many
  tools.
• A lot of web applications are using XML now.

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XML vs. HTML

• ltHTMLgt
• ltBODYgt
• ltULgt
• ltLIgt 1 kg apple
• ltLIgt 1/2 Sugar
• ltLIgt 1 kg white flour
• ltLIgt 250 g butter
• lt/ULgt
• ltPgt Place apples in a bowl.
• Toss with flour until covered. then, ...
• lt/BODYgt
• lt/HTMLgt

• ltRECIPEgt
• ltINGREDIENTSgt
• ltINGREDIENTgt 1Kg apple lt/INGREDIENTgt
• ltINGREDIENTgt 1/2Kg Sugar lt/INGREDIENTgt
• ltINGREDIENTgt 1 kg white flour
  lt/INGREDIENTgt
• ltINGREDIENTgt 250 g butter lt/INGREDIENTgt
• lt/INGREDIENTSgt
• ltINSTRUCTIONSgt
• ltINSTRUCTIONgt Place apples in a bowl.
• lt/INSTRUCTIONgt
• ltINSTRUCTIONgt Toss with flour until
  covered.
• lt/INSTRUCTIONgt
• .
• lt/INSTRUCTIONSgt
• lt/RECIPEgt

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XML

• Labels the data
• Structures the data
• Example

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Rules for Well-Formatted XML

• Every XML document must have a special tag lt?xml
  version1.0?gt to tell web browser it is an xml
  file
• Every XML document must have a single,
  all-enclosing root tag
• Every XML element must have a corresponding
  closing tag
• Just as HTML, XML elements must be properly
  nested
• XML tags are case sensitive, ltFOODgt and ltfoodgt
  are different
• The value of an attribute must appear in
  quotation marks (either double or single
  quotation marks work)

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XML Element Names

• Names can contain letters, numbers and other
  characters
• Names cannot begin with a number or an underscore
• Names cannot begin with the prefix XML or xml
  or xML etc.
• Names cannot contain spaces

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Good, Bad, and Unparsable

• Common errors in XML misspelling tag names, have
  more than one root-level element, forgetting to
  close an open quote
• If XML file is well-formed, the browser will
  display the file in a hierarchical fashion,
  otherwise, cannot load the file
• The XML file could be designed poorly although it
  is well-formed.

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Good, Bad and Unparsable

• Bad example
• ltTVGuidegt
• ltchannelgtlt/channelgt
• lttimegtlt/timegt
• lttitlegtlt/titlegt
• ltdescriptiongtlt/descriptiongt
• ltchannelgtlt/channelgt
• lttimegtlt/timegt
• lttitlegtlt/titlegt
• ltdescriptiongtlt/descriptiongt
• lt/TVGuidegt

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Good, Bad and Unparsable

• Solution
• ltTVGuidegt
• ltprogramgt
• ltchannelgtlt/channelgt
• lttimegtlt/timegt
• lttitlegtlt/titlegt
• ltdescriptiongtlt/descriptiongt
• lt/programgt
• ltprogramgt
• ltchannelgtlt/channelgt
• lttimegtlt/timegt
• lttitlegtlt/titlegt
• ltdescriptiongtlt/descriptiongt
• lt/programgt
• lt/TVGuidegt

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Design Tips

• Think logically and design accordingly
• Ex. Use ltCDgtlt/CDgt for cd collections
• If you want it, tag it
• Ex. Dont use ltTimegt1000pm
• ltnamegt..lt/namegt
• lt/Timegt
• Use ltTimegt ltslotgt1000pmlt/slotgt
• ltnamegtlt/namegt
• lt/Timegt
• Think generically
• Ex. Dont use ltNBCgtlt/NBCgt ltABCgtlt/ABCgt to group
  different networks
• Use ltnamegtNBClt/namegtltnamegtABClt/namegt
• Think hierarchically
• Start with a meaningful root element and work
  downward to successive levels of detail

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What is XSL?

• XSL is a language that allows one to describe for
  a browser how to process an XML file.
• XSL can convert an XML file into another format
  XML file.
• XSL can convert an XML file into a non-XML file.

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XSL

• The most common type of XSL processing is to
  convert XML file into HTML file which can be
  displayed by browsers. We will focus on this use
  of XSL.
• XSL is the bridge between XML and HTML.
• We can use XSL to have different HTML formats of
  the same data represented in XML.
• Separating data (contents) from style tags
  (display commands).
• Example