Displaying the XML document

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Displaying the XML document

• indicates covered in lecture/other slides to
  studied in your own time
• The e-commerce issues with the display of XML
• .xml files - how do we display the data they
  contain?
• Introduction to techniques
• XML Spy - How To
• Summary

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Our lifecycle the next stage

• XML documents built from XML Schema.
• XML document gets parsed into a node structure.
• Node structure is transformed into HTML using the
  stylesheet.

Parser stylesheet .xsl
Schema .xsd
Result HTML .html
XML doc .xml
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E-Commerce issues

• Web accessibility create alternative web sites
  for special needs e.g. disabilities, WAP phones,
  PDAs.
• Makes application data available to other
  applications supporting different schemas.
• Data transformation crucial! separation of
  transformation effort from application data
  effort good software engineering.
• Via transformation of the XML document, XML can
  be used as a lingua franca between different
  systems.
• This is akin to a Babelfish, i.e. an
  intermediate language that can be used to convert
  English to Chinese or (for our purposes) one
  companys data (and its structure/schema) to
  another companys.

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The presentation of XML

• XML (schemas and .xml files) may be understood by
  developers but what about the poor old user?
• XML information needs presenting in some other
  non-technical form typically via a browser
• On a PC
• On a mobile
• On a PDA
• On a TV
• Hence this week and next we are looking at the
  presentation aspects regarding XML.

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XSL and XSLT

• eXtensible Stylesheet Language (XSL).
• An XML based language.
• XSL Transformation (XSLT) - one subset of XSL but
  there are others.
• XSL and XSLT specify how an XML document should
  be converted (transformed) into other XML
  documents or text files, such a HTML, XHTML, or
  WML pages.
• XSL/XSLT also includes the ability to manipulate
  both tags and data content.

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A new file extension to consider

• .xsl files.
• XML Stylesheet files.
• Can be programmed actually quite complex
  there are now books devoted to just this aspect.
• Essential purpose to display the contents of an
  .xml file(s).
• It follows that an .xml file can have a
  stylesheet allocated to it .
• Just to mention that XML can use cascading
  stylesheets but for this module we will not.

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Other initial comments

• Stylesheet aspect of XML can be quite time
  consuming.
• Even using XML Spy this is no exception
  essentially as you will see you need to code
  it.
• XML Spy does assist in the selection of XSL
  items.
• Why is transformation necessary?
• Generally at the moment the main browsers are
  still HTML browsers and so typically the
  stylesheet converts the XML to display in an HTML
  format.
• In the future the overhead of the transformation
  will be reduced. A stylesheet will probably
  always be necessary however.

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More details about the terms

• Extensible Style Language (XSL) was the original
  specification.
• W3C divided XSL into two pieces
• XSLT for transformation.
• XSL-FO for formatting objects.
• Transforming an XML file (document) means in
  lay terms to analyse its contents and take action
  depending on the elements found i.e. display
  according to certain requirements programmed in
  the stylesheet.

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How to do it

• There are a number of methods for displaying XML.
  
• The following slides introduce the techniques.
• Transform using an XSL file and a parser
• SAX
• DOM
• Use data islands see last weeks notes

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The presentation of XML

• There are a range of options/alternatives but
  this is the main (current, general) technique
• Transform the XML by applying an XSL style sheet.
• The style sheet specifies how the XML should be
  parsed.
• Once the style sheet has been designed and
  created you need only to apply it to the xml file
  to get presentation output see XML Spy example
  later.
• To achieve the above a XSLT processor is needed -
  a .xml file and .xsl file are input and the
  output is transformed text.
• We need to use a parser and the choices include
  SAX or DOM more about this next week

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Parsers

• Parsing the XML using SAX (the Simple API for
  XML) server side.
• Originally developed for Java but Microsofts
  MSXML 4.0 also implements SAX.
• SAX reads XML like a spool of film running
  through a projector - as it finds elements it
  fires events that the developer can handle to
  derive the output desired.
• SAX yet works well with large XML files and hence
  is a server side solution.

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Parsers

• Parse the XML using DOM (Document Object Model)
  server side.
• DOM parser reads an XML file into memory and then
  traverse its nodes to extract the content.
• a node is one individual piece of information -
  an element - a node tree is hierarchical
  representation of the entire XML document.
• DOM is a rival to SAX and has an advantage over
  SAX
• DOM gives random access to the content rather
  than sequential.
• However, DOM can consume more memory that SAX and
  this may be a problem commercially.

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The presentation of XML

• Which one does XML Spy use by default?
• .xsl and the DOM parser and thats what we will
  use for this module.
• The following slides/screenshots explain.

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The steps involved

• 1. Create an XSL file a .xsl file.
• 2. Assign it to the XML file a .xml file.
• 3. Run the XSLT transformation processor.
• 4. View the results either in XML Spy or a
  browser.
• For home users you should find not difference
  to the labs but it you do let use know. You may
  need to download MSXML 3.0 if you are using IE
  older than 6.0 at home (i.e 5.0 or 5.5) this is
  explained on the next two screen grabs from XML
  Spy. May be time to upgrade your browser?
• The labs use the latest version (v7) and so it
  will not be necessary to download anything as the
  MSXML (the Microsoft DOM parser) 3.0 or 4.0 is
  built into the browser product.

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Create an XSL file a .xsl file
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Supporting notes

• When an .xsl file is created in XML Spy a default
  skeleton is created HOWEVER the body of the
  .xsl (the stylesheet) is NOT created
  automatically that is up to the developer to
  create/code.
• The stylesheet language (a specification) is used
  to populate the body part essentially the
  developer writes the stylesheet script
  indicating how the data will be displayed.

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Explanation of default skeleton

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltxslstylesheet version"1.0" xmlnsxsl"http//ww
  w.w3.org/1999/XSL/Transform" xmlnsfo"http//www.
  w3.org/1999/XSL/Format"gt
• create stylesheet code in here
• lt/xslstylesheetgt

This has to be written by the developer
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Explanation in more detail

• lt?xml version"1.0" encoding"UTF-8"?gt
• Every XSL style sheet is an XML document in
  itself and therefore should begin with a standard
  XML declaration.
• ltxslstylesheet version"1.0" xmlnsxsl"http//ww
  w.w3.org/1999/XSL/Transform" xmlnsfo"http//www.
  w3.org/1999/XSL/Format"gt
• Specifies a namespace for the style sheet.
• lt/xslstylesheetgt
• completes the style sheet.

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Supporting notes

• To start with dont worry about writing a
  stylesheet script.
• Let us move on to assigning an (empty) .xsl file
  to a .xml document.
• What we can then do is ask it to display the data
  in the .xml document what we will get is an
  .html file with nothing on it which is correct!
  As we have not specified how to display the data.
• However we must edit the stylesheet file so that
  it has the following line ltxsltemplate match"/"
  /gt - this will make it look for the root of the
  xml document we assign it to as depicted on the
  next screen grab.

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Assigning the .xsl to an .xml file

• Firstly within XML Spy open up (select) the .xml
  document you are going to use.
• Then click on the Assign XSL drop down menu
  option.
• Select Assign XSL XML Spy will ask you for the
  location of the .xsl file.
• The .xml file will be edited to include a line
  indicating the stylesheet it is to use.
• The following screen grabs illustrate.

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XSL
The XSL drop down menu
The .xml file we intend to use
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This shows in text view the xml file has now had
the .xsl file assigned to it
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Transformation stage

• Select the XSL Transformation option from the XSL
  drop down menu.
• Essentially this will parse the XML file with the
  .xsl stylesheet and create an .html file using
  the transformation engine.
• The display should show nothing! this proves
  you have everything in place (the environment is
  okay) the next stage will be to start to write
  a meaningful stylesheet!

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.html file created
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Views

• Can either view the result within XML Spy or by
  selecting the file in a browser such as IE.
• The following screen grab indicates this.

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XSLT

• More about the transformation engine can be found
  in XML Spy help.
• The next screen grab indicates this.

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Summary

• We have followed the next step of our lifecycle
  by creating a skeleton stylesheet (.xsl).
• We have then assigned it to an xml document.
• We have now entered the world of web browsers
  it most cases the user will wish to see the
  content of the xml document in a web browser -
  most browsers are HTML based but support XML.
• The browsers on the market all support XML to
  some extent
• Can you name 4 other browsers on the market?

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Summary

• In the future browsers will probably be XML
  browsers and some of the transformation process
  will be obsolete.
• The stylesheet can contain static data you may
  care to look at PODstyle2.xsl example on trentdev
  in the \studentinfo\Software\xml_for_deca_module
  \examplestylesheetsfolder to see what we mean
  by this notice how the stylesheet includes
  information normally found on a letterhead.

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Other related thoughts good topic for projects

• XML browsers versus HTML browsers
• Metrics regarding SAX V DOM
• B2B ecommerce impact of XSL/XSLT
• B2C ecommerce impact of XSL/XSLT
• Customised web-publishing with XSLT (particularly
  wrt legal changes in accessibility)