Week 7: More on XML XML Document Structure

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Week 7 More on XMLXML Document Structure

• XML Syntax rules define the low level structure
  of XML
• A Schema defines the higher level structure
• What tag names
• What each tag can contain
• XML Schema languages
• Document Type Definition (DTD)
• W3C XML Schema
• RelaxNG
• Schematron

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Document Type Definition (DTD)

• DTD defines
• What elements can be in an XML document.
• What attributes an element can have and
  restrictions on their values.
• What the content model for an element is what
  elements can occur within it and in what pattern.
  
• Where text can occur
• PCDATA -- parsed character data, entity
  references will be replaced
• CDATA -- character data, can contain special
  characters
• Why use a DTD
• To enforce a standard that many people can rely
  on (for example, XHTML).
• To provide structure for document authors to work
  within (for example, Docbook).
• To enable validation of documents.

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XML example

• lt?xml version'1.0'?gt lt!DOCTYPE slides SYSTEM
  "slides.dtd"gt ltslidesgt ltfoilgt lttitlegtXML
  Basicslt/titlegt
• ltitemizedlistgt ltlistitemgt XML is a standard
  for defining markup languages. lt/listitemgt
  ltlistitemgt XML defines the ltemphasisgt syntax
  lt/emphasisgt of markup. lt/listitemgt
  lt/itemizedlistgt lt/foilgt lt/slidesgt

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DTD example

• lt!ELEMENT slides (foilsection)gt
• lt!ATTLIST slides "label CDATA IMPLIED
  status CDATA IMPLIED id ID IMPLIEDrevisionfl
  ag (changed added deleted off) IMPLIED"gt
• lt!ELEMENT section (title,foil)gt
• lt!ELEMENT foil (title,(itemizedlistpara))gt
• lt!ELEMENT itemizedlist (listitem)gt
• lt!ELEMENT listitem PCDATAgt
• lt!ELEMENT para PCDATAgt
• lt!ENTITY elec3609 ELEC3609(Web Technology)"gt
• lt!ENTITY copy "x00A9"gt

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Declaring Elements

• The form of an element declaration
• lt!ELEMENT element_name (names of child elements)gt
• Example
• lt!ELEMENT slides (foilsection)gt
• Modifiers can be added to child element
  specifications
• one or more occurrences
• zero or more occurrences
• ? zero or one occurrence.
• If an element just contains text then its content
  model is just PCDATA

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Declaring Attributes

• The form of an attribute declaration
• lt!ATTLIST element_name attribute_name
  attribute_type default_valuegt
• For example
• lt!ATTLIST slides label CDATA IMPLIEDgt
• Possible default values for attributes are
• a value - the value used, if none is specified in
  an element
• FIXED - the value, which every element will have
  and which cannot be changed
• REQUIRED - no default value is given every
  instance of the element must specify a value
• IMPLIED - no default value is given the value
  may or may not be specified in an element.

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Declaring Entities

• Entities can be defined so that they can be
  referenced anywhere in the content.
• The form of an entity declaration
• lt!ENTITY entity_name "entity_value"gt
• You can define an entity to represent a string
• lt!ENTITY elec3609 ELEC3609 (Web Technology)"gt
• In an XML document the string can be referenced
  by
• I'm studying elec3609

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What DTDs Can't Do

• Can't say anything about the textual content of
  an element.
• XML Schema proposals attempt to do this (XML
  Schema, RELAX-NG).
• Equivalent to providing a (programming language)
  type system for XML.
• RSS Really Simple Syndication
• RSS is a standard format for web site summaries.
• An RSS summary, at a minimum, is a document
  describing a "channel" consisting of
  URL-retrievable items. Each item consists of a
  title, link, and brief description. (RSS
  Specification) http//cyber.law.harvard.edu/rss/rs
  s.html
• RSS defines a set of standard metadata elements
  for describing web resources (in particular, news
  feeds).
• Recently Atom has been proposed as a successor to
  RSS http//www.atomenabled.org/

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RSS example

• ltxml version"1.0" encoding"ISO-8859-1"?gt ltrss
  version"0.91"gt
• ltchannelgt
• lttitlegtAnnouncements for ELEC3609lt/titlegt
• ltlinkgthttp//www.eelab.usyd.edu.au/ELEC3609/cgi-b
  in/newslt/linkgt
• ltdescriptiongt
• This is an news service for ELEC3609 unit.
• lt/descriptiongt
• ltlanguagegten-uslt/languagegt
• ltitemgt
• lttitlegtAssignment 3lt/titlegt
• ltlinkgthttp//www.eelab.usyd.edu.au/ELEC3609/cgi-bi
  n/ass3.txtlt/linkgt
• ltdescriptiongt Assignment 3 is now available.
  lt/descriptiongt
• lt/itemgt
• lt/channelgt
• lt/rssgt

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XML Bookmark Exchange Language

• Web browsers store bookmarks in a variety of
  formats, some provide tools to import bookmarks
  from other browsers, but often you can't go back
  again.
• XBEL acts as an intermediate format between the
  Internet Explorer, Netscape and other formats.
• Bookmarks organised into folders.
• Bookmark entries and folders can have various
  properties encoded as sub-elements title,
  description, info, metadata.
• Bookmark url is stored as an attribute

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XSBEL example

• lt?xml version"1.0"?gt
• lt!DOCTYPE xbel PUBLIC "//IDN python.org//DTD XML
  Bookmark Exchange Language 1.0//EN//XML"
  "http//www.python.org/topics/xml/dtds/xbel-1.0.dt
  d"gt
• ltxbelgt
• ltinfogt
• ltmetadata owner"Norman Walsh ltndw_at_nwalsh.comgt"
  /gt
• lt/infogt
• ltfolder id"perlbookmarks"gt
• lttitlegtPerllt/titlegt
• ltbookmark href"http//www.perl.com/"gt
• lttitlegtPerl.comlt/titlegt lt/bookmarkgt
• ltbookmark href"http//www.activestate.com/"gt
• lttitlegtActiveState Tool Corp. (Perl for
  Win32)lt/titlegt lt/bookmarkgt
• lt/foldergt
• lt/xbelgt

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VoiceXMLhttp//www.w3.org/TR/voicexml20/

• VoiceXML is an XML-based markup language for the
  development of voice applications.
• Using only a traditional Web infrastructure, you
  can create applications that are accessible over
  the telephone.
• VoiceXML is designed for creating audio dialogs
  that feature synthesized speech, digitized audio,
  recognition of spoken and DTMF key input,
  recording of spoken input, telephony, and mixed
  initiative conversations

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VoiceXML example

• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltvxml version"2.0" lang"en"gt
• ltformgt
• ltfield name"city"gt ltpromptgt Where do you want
  to travel to? lt/promptgt ltoptiongt Edinburgh
  lt/optiongt ltoptiongt New York lt/optiongt ltoptiongt
  London lt/optiongt ltoptiongt Paris lt/optiongt
  ltoptiongt Stockholm lt/optiongt lt/fieldgt
• ltfield name"travellers" type"number"gt
• ltpromptgt How many are travelling to ltvalue
  expr"city"/gt? lt/promptgt lt/fieldgt
• ltblockgt ltsubmit next"http//localhost/handler"
  namelist"city travellers"/gt lt/blockgt
• lt/formgt
• lt/vxmlgt

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XML on the Web - AJAX

• AJAX - Asynchronous Javascript and XML
• Javascript makes a request to the server from
  within a page
• Recieves an XML response, updates the page using
  the contents
• XML is a data exchange language, easily parsed by
  Javascript
• But, is there a better alternative?
• JSON
• Javascript Object Notation http//www.json.org/
• Use Javascript as a data exchange language
• No need to parse it, just evaluate and you have
  the data JSON

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XML vs. JSON

• JSON is purely for data interchange
• XML is more general a markup langauge
• JSON needs no parser - unless you want to be
  secure
• XML allows for validation independent of the
  application
• JSON is easier to write code for in Javascript
• XML is better when there might be more than one
  kind of consumer for the data

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JSON

• "Name" "John Smith", "address"
  "streetAddress" "21 2nd Street", "city" "New
  York", , "phoneNumbers" "212 555-1234", "646
  555-4567"

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Parsing XML in Javascripthttp//www.w3schools.com
/Xml/xml_parser.asp

• var parsernew DOMParser()
• var docparser.parseFromString(txt,"text/xml")
  / now access elements using the DOM API / to
  doc.getElementsByTagName("to")0.childNodes0.no
  deVal

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Parsing JSON in Javascript

• var p eval("(" JSON_text ")")
• / or using a parser (safer) /
• var p json_parse(JSON_text)
• / now access the data elements /
• to p.to

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Summary

• XML is a simple markup language with hierarchical
  structure.
• Documents can be shown to be well formed or
  valid.
• DTD allows standard document types to be defined
  (eg. XHMTL).
• JSON is an alternative data format for sending
  data structures to web browsers.
• Parsers process the XML or JSON to give programs
  access to the data