The Extensible Markup Language XML

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The Extensible Markup Language (XML)

• By Raghu Garudadri

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Dont break the seal
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Agenda

• What is XML ?
• Why XML?
• XML goals
• Underlying theory
• DTD/Example DTD/Example XML Document
• XML Vs. HTML
• Advantages and Disadvantages of XML over HTML
• XML application areas
• Will XML replace HTML
• References and additional Information
• Q A

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What is XML?

• Extensible Markup Language (XML) is a language
  for documents containing structured information
• It separates the content of the document from its
  appearance
• Worldwide Web Consortium (W3C) specification
• Status recommendation
• Original version 1996
• Subset of the Standard Generalized Markup
  Language (SGML)
• Simpler than SGML
• More appropriate for the Internet
• Cousin of the Hypertext Markup Language
  (HTML),goes beyond the current limitations of
  HTML

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Why XML?

• HTML, comes bound with a set of semantics and
  does not provide arbitrary structure.
• SGML provides arbitrary structure, but is too
  difficult to implement just for a web browser
• XML was created so that richly structured
  documents could be used over the web
• The only viable alternatives, HTML and SGML, are
  not practical for this purpose.

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Goals set for XML by the W3C

• XML shall be straightforwardly usable over the
  Internet
• XML shall support a wide variety of applications
• XML shall be compatible with SGML
• It shall be easy to write programs that process
  XML documents
• The number of optional features in XML is to be
  kept to the absolute minimal, ideally zero
• XML documents should be human-legible and
  reasonably clear
• XML design should be prepared quickly

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Goals contd..

• The design of XML should be formal and concise
• XML documents shall be easy to create
• Terseness in XML markup is of minimal importance

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Underlying Theory

• Terminology commonly used with XML
• Content
• Alias character data
• The documents raw data
• Structure
• Description of how the content is organized
• Within an XML document, structure is indicated by
  tags
• Presentation
• Description of how the document should be
  rendered. XML does NOT specify presentation!!!

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Extensible

• Set of tags is
• Not closed
• "Extensible"
• Not specified by the XML language
• Specified by the user via a DTD (Document Type
  Definition)

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Markup

• An XML document contains "character data" and
  "markup"
• Character data
• The raw data of the document
• Markup
• Start tags
• ltfilmgt
• lttitlegt
• End tags
• lt/ filmgt
• lt/ titlegt
• Comments
• lt!-- This is a comment. --gt
• Processing instructions (instructions to parser
  or application)
• lt? xml version "1.0" ?gt
• Start tags and end tags specify the structure of
  an XML document

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DTD

• XML is a metalanguage, it doesnt define actual
  tags
• DTD (Document Type Definition) defines actual
  tags and structures

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Example DTD

• In file film- guide. dtd
• 1. lt! ELEMENT film- guide (film)gt
• 2. lt! ELEMENT film (title, run- time, stars)gt
• 3. lt! ELEMENT title ( PCDATA)gt
• 4. lt! ELEMENT run- time ( PCDATA)gt
• 5. lt! ELEMENT stars (name)gt
• 6. lt! ELEMENT name ( PCDATA)gt
• Informal description
• Line 1 A "film- guide" tag contains 0 or more
  "film" tags
• Line 2 A "film" tag contains a "title" tag,
  followed by a "run- time" tag, followed by a
  "stars" tag
• Line 3 A "title" tag contains parsed character
  data
• Line 4 A "run- time" tag contains parsed
  character data
• Line 5 A "stars" tag contains 0 or more "name"
  tags
• Line 6 A name tag contains parsed character data

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Example XML Document

• In file film- guide. xml
• 1. lt? xml version" 1.0"?gt
• 2. lt! DOCTYPE film- guide SYSTEM "film- guide.
  dtd"gt
• 3. ltfilm- guidegt
• 4. ltfilmgt
• 5. lttitlegt Citizen Kanelt/ titlegt
• 6. ltrun- timegt 119lt/ run- timegt
• 7. ltstarsgt
• 8. ltnamegt Joseph Cottonlt/ namegt
• 9. ltnamegt Orsen Wellslt/ namegt
• 10. lt/ starsgt
• 11. lt/ filmgt
• 12. ltfilmgt
• 13. lttitlegt The Godfatherlt/ titlegt
• 14. ltrun- timegt 125lt/ run- timegt
• 15. ltstarsgt
• 16. ltnamegt Marlon Brandolt/ namegt
• 17. ltnamegt Al Pacinolt/ namegt
• 18. ltnamegt Robert Duvalllt/ namegt

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XML Vs. HTML

• Other than both being derived from SGML, XML(a
  subset of SGML)
• and HTML(written in SGML) are not really
  comparable
• HTML is optimized for easy learning
• Has evolved into a markup language that describes
  the look, feel and action of a web page
• Is for output to a web browser (presentation)
• One tag set for all applications
• Predefined semantics for each tag
• Predefined data structures
• No formal validations
• well suited for simple applications
• In contrary, XML
• doesnt describe how a page looks, how it acts or
  what it does. XML describes what the words in a
  document are
• Separates structure and display of data
• documents are more portable and can be used in
  many demanding applications like
• Large or complex data collections
• Data that must be used in different ways
• Data with a long life cycle
• Data intended to drive Java applets and other
  programs

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XML Vs. HTML Contd..

• 1. ltHTMLgt
• 2. ltHTMLgt
• 3. ltTITLEgt Film Guidelt/ TITLEgt
• 4. ltBODYgt
• 5. ltH2gt Film Guidelt/ H2gt
• 6. ltHRgt
• 7. ltBgt Film lt/ Bgt Citizen Kanelt BRgt
• 8. ltBgt Running Time lt/ Bgt 119lt BRgt
• 9. ltBgt Stars lt/ Bgt
• 10. ltULgt
• 11. ltLIgt Joseph Cottonlt/ LIgt
• 12. ltLIgt Orson Wellslt/ LIgt
• 13. lt/ ULgt
• 14. ltHRgt
• 15. ltBgt Film lt/ Bgt The Godfatherlt BRgt
• 16. ltBgt Running Time lt/ Bgt 125lt BRgt
• 17. ltBgt Stars lt/ Bgt
• 18. ltULgt
• 19. ltLIgt Marlon Brandolt/ LIgt

• In file film- guide. xml
• 1. lt? xml version" 1.0"?gt
• 2. lt! DOCTYPE film- guide SYSTEM "film- guide.
  dtd"gt
• 3. ltfilm- guidegt
• 4. ltfilmgt
• 5. lttitlegt Citizen Kanelt/ titlegt
• 6. ltrun- timegt 119lt/ run- timegt
• 7. ltstarsgt
• 8. ltnamegt Joseph Cottonlt/ namegt
• 9. ltnamegt Orsen Wellslt/ namegt
• 10. lt/ starsgt
• 11. lt/ filmgt
• 12. ltfilmgt
• 13. lttitlegt The Godfatherlt/ titlegt
• 14. ltrun- timegt 125lt/ run- timegt
• 15. ltstarsgt
• 16. ltnamegt Marlon Brandolt/ namegt
• 17. ltnamegt Al Pacinolt/ namegt
• 18. ltnamegt Robert Duvalllt/ namegt

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Advantages of XML over HTML

• Flexibility of defining own markup language will
  help to code documents more precisely
• Reflects structures and semantics of documents
• Better searching and navigation
• Allows single document to be used many ways

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Disadvantages of XML over HTML

• More difficult, demanding, and precise than HTML
• Still in experimental/evolution stages
• Lack of browser support/end user applications

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XML Application Areas

• There are Two primary use of XML
• Publishing
• Data Communication

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XML for Publishing
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Benefits of XML for Publishing

• Same XML document can be presented in multiple
  ways
• Presentation medium is Browser gt
• present document as HTML
• Presentation medium is word processor gt
• present document using word processor format
• Presentation medium is Braille reader gt
• present document as raised dots
• Presentation medium is speech generator gt
• present document as sound waves
• Multiple XML documents can be presented in the
  same way
• Book written by author1 can be presented using
  precisely the same format as books written by
  author2, author3, etc.
• Newspaper publisher can collect articles from
  disparate sources, and publish them in one
  consistent format

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XML for Data Communication
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Benefits of XML for Data Communication

• Extensible
• Using a DTD, you define the protocol
• Simple
• Easy to understand
• Tree structured
• Human readable
• Easy to debug
• Standard
• The mechanism for defining the protocol (DTD) is
  standardized
• Business communities are defining standard DTDs
  (publishing, pharmaceuticals, financials, etc.)
• Commercial XML parsers/ generators are readily
  available -- for free!!!

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XML enables data sharing

• XML is suitable for exchanging information
• XML provides structure for data

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Business applications of XML

• Supply chain management connects trading
  partners,suppliers and customers
• E-commerce applications enables automation and
  integration of backend databases, ERP systems,
  etc., and facilitates presentation of XML data as
  html vis XSL(Extensible Stylesheet Language)
• EDI translation of EDI documents to XML allows
  for new B2B applications and broadens the supply
  chain
• ERP allows access to business logic and data
  embedded in ERP systems
• Legacy system integration exposes legacy data
  to web applications

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XML in Web browsers

• XML is going to be an integral part of the web
• Microsoft jumped in quickly and implemented XML,
  IE5 and above supports XML
• Netscape was late, but it is trying to catch up.

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Importance of XML

• Next generation web architecture
• Provides means to solve data interchange problems
• Standards based
• Has wide spread industry support
• Based on SGML experience

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What problems does XML solve?

• Multiple output formats
• Information exchange between software systems
• Long term format for information archives

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Will XML replace HTML?

• The Answer is NO.
• XML will coexist with HTML
• XML does not specify the format or appearance of
  a document.
• An emerging standard XSL (Extensible Stylesheet
  Language) specifies the appearance of a document.
  You can think of XSL translating XML into HTML
  for display.
• XML is a good viable alternative for high-end
  publishing on the web but it is not a replacement
  for HTML

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References and additional Information

• URLs
• XML Standards
• http//www.w3.org/XML - the core site for the XML
  standards body
• XML Forums and Information hubs
• http//www.xml.com - an excellent site for XML
  information, sponsored by Seybold
• http//www.xmlinfo.com - general XML resources
  site
• http//xmlrepository.com - general XML resource
  site
• http//www.geocities.com/WallStreet/Floor/5815 -
  the XML/EDI group
• http//www.infotek.no/sgmltool/guide.htm - XML
  and SGML products and companies
• http//www.ucc.ie/xml - XML FAQ maintained by key
  people in XML standards groups
• http//www.geocities.com/SiliconValley/Peaks/5957/
  xml.html - a small XML info site
• http//www.xmlx.com - commerce Nets XML
  Exchange.
• http//www.csclub.uwaterloo.ca/u/relander/XML -
  general XML information
• http//www.oasis-open.org/cover/xml.html - OASIS
  XML cover pages
• http//ala.vsms.nottingham.ac.uk/vsms/java -
  On-line course covering Java and XML
• http//www.jclark.com/xml - James Clarks XML
  resources
• http//www.sil.org/sgml - Brian Covers SGML/XML
  page
• http//www.geocities.com/SiliconValley/Peaks/5957/
  xml.html - general XML information
• http//www.simonstl.com - general XML information

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Conclusion

• The extensible markup language (XML) has been
  referenced
• as the universal duct tape for all the software
  integration problems,
• it is quickly becoming a accepted industry
  standard. Almost any
• platform can Manipulate XML allowing companies to
  build
• business-to-business systems with out vendor
  lock-in and with the
• Infrastructure they already have. Lets hope XML
  will enable
• competitive but coordinated markets