CSE 190: Internet ECommerce

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CSE 190 Internet E-Commerce

• Lecture 17 XML, XSL

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Problem Communicating data

• Consider A merchant, like Amazon, wants to
  publish its catalog of books on sale to a third
  party (e.g. a book club), so that party can
  create a newsletter using the data.
• Question What format does Amazon put that data
  in? How do we communicate that format to the
  third party?

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Some Approaches

• Define binary format based upon some structure.
  Distribute a Word document describing the layout
  of the fields.struct Book char isbn 40
  char authorFirstName 60 char
  authorLastName 60 float salePrice
  enum SHIPPING_AVAILABILITY IN_STOCK, SOLD_OUT
  Limitation Adding a new field means
  the parsing code must change takes weeks for
  programmers to read the specification and write
  the parser future applications like this require
  equal amounts of work.

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Some Approaches

• 2. Output the data in HTML, send a Word document
  describing the layout of the data. Ex
• lthtmlgtltheadgtlt/headgtltbodygt
• lttablegt
• lttheadgtlttrgtltthgtTitlelt/thgtltthgtISBNlt/thgtltthgtAuthorlt/
  thgtltthgtPricelt/thgtlt/trgt
• lttrgtlttdgtFast Food Nationlt/tdgtlttdgt234234234lt/tdgtlttd
  gtEric Schlosserlt/tdgtlttdgt17.50lt/tdgtlt/trgt
• Evaluation
• At least we can use the HTML parser to get the
  data
• Still have to parse the resulting HTML tree to
  get data
• Adding new data fields still implies writing more
  parse code

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Approach Common syntax with user defined tags

• Use a strict syntax for tags, but allow any tag
  name to be used
• ltbooklistgt
• ltbook isbn0395977894gt
• lttitlegtFast Food Nationlt/titlegt
• ltauthorgtEric Schlosserlt/authorgt
• ltPricegt17.50lt/Pricegt
• ltbook isbn1406066985gt .
• Evaluation
• Directly expresses the data we wanted to
  communicate
• May re-use the same parser for many different
  applications
• Easy to ignore unfamiliar tags
• Call it XML Exchange Markup Language

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What is XML?

• XML Used to communicate data to machines.
• HTML Used to communicate documents to people.
• XML An application of SGML (a document type
  description language)
• Unlike HTML, you may invent your own tags
• Uses a strict syntax so that XML parsers may be
  reused for many applications
• Unknown tags and attributes are ignored
• May be used to separate content from presentation
  by applying a transformation to the data to
  create a readable document.
• Written in plain-text files human-readable, not
  binary

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XML Example

• Show me the list of books on sale.
• lt?xml version1.0 ?gt
• ltbooklistgt
• ltbook isbn234234234gt
• lttitlegtFast Food Nationlt/titlegt
• ltauthorgtEric Schlosserlt/authorgt
• ltpricegt17.50lt/pricegt
• ltin_stock /gt
• lt/bookgt
• ltbook isbn456465465gt
• lttitlegtReligion Explainedlt/titlegt
• ltauthorgtPascal Boyerlt/authorgt
• ltpricegt24.99lt/pricegt
• ltout_of_stock /gt
• lt/bookgt
• lt/booklistgt

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XML Example

• Show me the grades of all students.
• lt?xml version1.0gt
• ltstudentgradesgt
• ltstudent idA02111111gt
• ltexam1gt15lt/exam1gt
• ltexam2gt15lt/exam2gt
• ltprojectgt16lt/projectgt
• ltfinal makeupyesgt14lt/finalgt lt/studentgt
• ltstudent idA02222222gt
• ltexam1gt15lt/exam1gt
• ltexam2gt15lt/exam2gt
• ltprojectgt16lt/projectgt
• ltfinal makeupnogt15lt/finalgt lt/studentgt
• lt/studentgradesgt

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XML Syntax

• Written in plain text (using notepad, e.g.)
• All elements must have a closing tag
• Ex ltpgtText text textlt/pgt
• Forbidden ltpgtLine OneltpgtLine Two
• Single element tags close themselves
• Ex ltbr /gt
• Not ltbrgttext text or ltbr /gttext textlt/brgt
• Should start with an XML document indicator
• Ex lt?xml version1.0?gt
• Has one root element, the first in the document
• All attribute values must be single or double
  quoted
• Ex ltboat_ride price15.00 /gt
• Not ltboat_ride price15.00 /gt
• Not ltimage_size width100 /gt
• Tags are case sensitive
• Ex ltauthorgtEric Schlosserlt/authorgt
• Not ltauthorgtEric Schlosserlt/Authorgt
• Mime Type text/xml

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Parsing

• An XML parser may parse any XML document
• Well-formed XML document follows the XML syntax
  rules
• Valid XML document conforms to its specified DTD
  (Document Type Definition)
• lt?xml version"1.0 ?gt
• lt!DOCTYPE note SYSTEM "note.dtd"gt
• ltnotegt
• lttogtMannylt/togt
• ltfromgtJannilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt

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DTDs

• DTDs Describe the allowable tags and attributes
  used in an XML document
• lt!DOCTYPE TVSCHEDULE
• lt!ELEMENT TVSCHEDULE (CHANNEL)gt
• lt!ELEMENT CHANNEL (BANNER,DAY)gt
• lt!ELEMENT BANNER (PCDATA)gt
• lt!ELEMENT DAY (DATE,(HOLIDAYPROGRAMSLOT))gt
• lt!ELEMENT HOLIDAY (PCDATA)gt lt!ELEMENT DATE
  (PCDATA)gt
• lt!ELEMENT PROGRAMSLOT (TIME,TITLE,DESCRIPTION?)gt
  
• lt!ELEMENT TIME (PCDATA)gt lt!ELEMENT TITLE
  (PCDATA)gt 
• lt!ELEMENT DESCRIPTION (PCDATA)gt
• lt!ATTLIST TVSCHEDULE NAME CDATA REQUIREDgt
• lt!ATTLIST CHANNEL CHAN CDATA REQUIREDgt
• lt!ATTLIST PROGRAMSLOT VTR CDATA IMPLIEDgt
• lt!ATTLIST TITLE RATING CDATA IMPLIEDgt
• lt!ATTLIST TITLE LANGUAGE CDATA IMPLIEDgt
• gt
• Written in SGML

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Namespaces

• Question How do we create a document using tags
  from two different DTDs?
• We can just combine the two, using the tags from
  both DTDs
• Problem What if both DTDs are using the same tag
  name to refer to different items?
• Solution We can specify what namespace a tag is
  coming from.
• Namespaces Specify the DTD that a tag name is
  relative to
• Example
• lt?xml version1.0?gt
• ltamznbooklist xmlnsamznhttp//www.amazon.com/d
  eals/BLgt
• ltamznbook isbn23423422gt
• ltamznauthorgtEric Schlosserlt/amznauthorgt
• ltloccategory xmlnslochttp//www.libraryofco
  ngress.org/classifygt Food,
  muckrakinglt/loccategorygt
• ltamznpricegt17.50lt/amznpricegt
• lt/amznbookgt
• lt/amznbooklistgt

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Viewing XML

• XML documents may be viewed natively in IE,
  Netscape
• Ex testdoc.xml
• What if wed like to present the data to people,
  in a more readable way?
• Useful for creating data documents, then a
  clearly separated way for viewing the data
• XML Transformation into a view
• CSS
• XSLT

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CSS

• CSS Cascading Style Sheets
• Applied to XML, similar to HTML
• Example (note the tags in the selector)
• CATALOG background-color ffffff width 100
  
• CD display block margin-bottom 30pt
  margin-left 0
• TITLE color FF0000 font-size 20pt
• ARTIST color 0000FF font-size 20pt
• COUNTRY,PRICE,YEAR,COMPANY display block
  color 000000 margin-left 20pt
• Limitation Not all browser versions support XML
  CSS display

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XSL

• XSL XML Style Language
• Provides declarative method for transform XML
  document into a viewable format (usually HTML)

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XSL Example

• lt?xml version"1.0 ?gt
• ltxslstylesheet version"1.0 xmlnsxsl"http//ww
  w.w3.org/1999/XSL/Transform"gt
• ltxsltemplate match"/"gt
• lthtmlgt
• ltbodygt
• lttable border"1"gt
• lttrgt
• ltthgtTitlelt/thgt
• ltthgtArtistlt/thgt
• lt/trgt
• ltxslfor-each select"catalog/cd"gt
• lttrgt
• lttdgtltxslvalue-of select"title" /gtlt/tdgt
• lttdgtltxslvalue-of select"artist" /gtlt/tdgt
• lt/trgt
• lt/xslfor-eachgt
• lt/tablegt
• lt/bodygt
• lt/htmlgt

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XSL Elements

• xsltemplate
• Replaces all elements matching the Xpath
  expression (e.g. / matches all elements) with
  the specified content
• xslfor-each
• For each element matching the select Xpath
  expression, the element is replaced with the
  specified content
• xslvalue-of
• Is replaced with the text value of the element
  specified by selects Xpath expression
• Xpath A pattern language for XML
• / -gt matches all elements
• a/b -gt matches all A elements with children of
  tag B

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XSL, Server-Side

• XML file may be made human-friendly by specifying
  style sheet from within the XML document
• Uses client-side support to transform into HTML
• What if the browser doesnt support this?
• The web server may do the transformation on the
  server side, giving the browser the resulting
  HTML.
• May decide to detect the browser version before
  deciding on what method to use

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References

• Book Step by Step XML by Michael Young
• URL http//www.w3schools.com/xml/
• URL http//www.w3schools.com/xsl/